[U-Boot-Users] Ideas on U-Boot configuration with FDT

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Grandegger]

Hello,

here are my ideas on what is basically necessary to use FDT for U-Boot 
configuration. I tried to keep it simple:

- If CFG_FDT_ADDR is defined in the boards configuration file, the
   global variable "fdt", already used by the FDT command, will be set
   at compile time to that address:

     #ifdef CFG_FDT_ADDR
             struct fdt_header *fdt = CFG_FDT_ADDR;
     else
             struct fdt_header *fdt = NULL;
     #endif

- In the early boot phase, before relocation, the FDT is checked and an
   error message printed in case it's not found or invalid:

     CPU:  MPC5200 v1.0, Core v1.1 at 396 MHz
           Bus 132 MHz, IPB 66 MHz, PCI 33 MHz
     FDT:  FDT_ERR_BADMAGIC (or OK, or version number?)

    At this level also the compatibility of the FDT tree could be checked
    using fdt_boardcheck().

- After relocation, the blob is copied into memory via fdt_open_into()
   to a defined place and "fdt" is updated accordingly. Not sure, what
   location in RAM to use, but it should fit into the existing scheme.
   Any recommendations?

- When U-Boot is up, "fdt" points to a valid FDT, e.g. "fdt addr" is not
   necessary.

- I think the basic mechanism should also work _without_ FDT commands
   (cmd_fdt.c, getting ride of quit some code).

- bootm should then automatically use the address of "fdt" to boot the
   kernel.

Some more comments. I realized rather heavy consistency checks on almost 
any public FDT function via fdt_check_header. I actually would prefer to 
have one extended check function at the beginning, which also ensures 
the compatibility with the board and reduce the other checks to just 
verify the magic number.

Other related issues? Do we also need to maintain a checksum of the 
blob? At least it's on Jerry's to-do list.

What do you think? I'm going to show a first patch soon.

Wolfgang.

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Timur Tabi]

Wolfgang Grandegger wrote:

>      CPU:  MPC5200 v1.0, Core v1.1 at 396 MHz
>            Bus 132 MHz, IPB 66 MHz, PCI 33 MHz
>      FDT:  FDT_ERR_BADMAGIC (or OK, or version number?)
> 
>     At this level also the compatibility of the FDT tree could be checked
>     using fdt_boardcheck().

I think fdt_checkboard() (or boardcheck) should be run from inside the fdt_open_into() 
command.  This takes advantage of the existing mechanism of fdt_open_into() to return an 
error.  It also allows for a device tree to be opened after U-Boot has booted.

> - After relocation, the blob is copied into memory via fdt_open_into()
>    to a defined place and "fdt" is updated accordingly. 

So we'll need to have CFG_FDT_ADDR_FLASH and CFG_FDT_ADDR_RAM.

> Not sure, what
>    location in RAM to use, but it should fit into the existing scheme.
>    Any recommendations?
> 
> - When U-Boot is up, "fdt" points to a valid FDT, e.g. "fdt addr" is not
>    necessary.

I think this feature needs to be optional.  That is, if CFG_FDT_ADDR_xxx are defined, then 
we can enable this feature.  Otherwise, fdt_addr will still be necessary.  Remember, we'll 
still need to support architectures that don't have device trees.

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Grandegger]

Timur Tabi wrote:
> Wolfgang Grandegger wrote:
> 
>>      CPU:  MPC5200 v1.0, Core v1.1 at 396 MHz
>>            Bus 132 MHz, IPB 66 MHz, PCI 33 MHz
>>      FDT:  FDT_ERR_BADMAGIC (or OK, or version number?)
>>
>>     At this level also the compatibility of the FDT tree could be checked
>>     using fdt_boardcheck().
> 
> I think fdt_checkboard() (or boardcheck) should be run from inside the 
> fdt_open_into() command.  This takes advantage of the existing mechanism 
> of fdt_open_into() to return an error.  It also allows for a device tree 
> to be opened after U-Boot has booted.

But it's too late for initial initialization (before RAM is available). 
Using the FDT directly from ROM is not recommended because access might 
be slow, but we likely need it for early initialization.

>> - After relocation, the blob is copied into memory via fdt_open_into()
>>    to a defined place and "fdt" is updated accordingly. 
> 
> So we'll need to have CFG_FDT_ADDR_FLASH and CFG_FDT_ADDR_RAM.

OK.

>> Not sure, what
>>    location in RAM to use, but it should fit into the existing scheme.
>>    Any recommendations?
>>
>> - When U-Boot is up, "fdt" points to a valid FDT, e.g. "fdt addr" is not
>>    necessary.
> 
> I think this feature needs to be optional.  That is, if CFG_FDT_ADDR_xxx 
> are defined, then we can enable this feature.  Otherwise, fdt_addr will 
> still be necessary.  Remember, we'll still need to support architectures 
> that don't have device trees.

Exactly, that's also what I meant.

Wolfgang.

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Timur Tabi]

Wolfgang Grandegger wrote:

>> I think fdt_checkboard() (or boardcheck) should be run from inside the 
>> fdt_open_into() command.  This takes advantage of the existing 
>> mechanism of fdt_open_into() to return an error.  It also allows for a 
>> device tree to be opened after U-Boot has booted.
> 
> But it's too late for initial initialization (before RAM is available). 

Just make it so that fdt_open_into() is called early:

	checkboard,
	INIT_FUNC_WATCHDOG_INIT
#if defined(CFG_FDT_ADDR_FLASH)
	init_fdt,
#endif
#if defined(CONFIG_MISC_INIT_F)
	misc_init_f,
#endif
	INIT_FUNC_WATCHDOG_RESET
#if defined(CONFIG_HARD_I2C) || defined(CONFIG_SOFT_I2C)
	init_func_i2c,
#endif

and init_fdt() calls fdt_open_into().

> Using the FDT directly from ROM is not recommended because access might 
> be slow, but we likely need it for early initialization.

I don't access speed is important for the reading the FDT, especially flash vs. RAM.  It's 
not that much slower.

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Timur Tabi]

Wolfgang Grandegger wrote:

> RAM is _not_ available at that stage.

Do we really need RAM to parse the device tree and configure U-Boot?  I think not.

The device tree has a memory section:

	memory {
		device_type = "memory";
		reg = <00000000 10000000>;	// 256MB
	};

So the question is: do we want U-Boot to use this node to determine how much RAM there is, 
or do we want U-Boot to determine how much RAM there is and update this node?

> Depends, you might be right for FLASH on a 32-bit bus. On slow ROM 
> devices and slow processors, it matters.

I still don't see how it's important.  If the device tree is on slow memory, so what?  You 
have to read it sooner or later.  If your board can't handle this feature, then don't 
enable it, and configure U-Boot the "old fashioned way".

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Grandegger]

Timur Tabi wrote:
> Wolfgang Grandegger wrote:
> 
>>> I think fdt_checkboard() (or boardcheck) should be run from inside 
>>> the fdt_open_into() command.  This takes advantage of the existing 
>>> mechanism of fdt_open_into() to return an error.  It also allows for 
>>> a device tree to be opened after U-Boot has booted.
>>
>> But it's too late for initial initialization (before RAM is available). 
> 
> Just make it so that fdt_open_into() is called early:
> 
>     checkboard,
>     INIT_FUNC_WATCHDOG_INIT
> #if defined(CFG_FDT_ADDR_FLASH)
>     init_fdt,
> #endif
> #if defined(CONFIG_MISC_INIT_F)
>     misc_init_f,
> #endif
>     INIT_FUNC_WATCHDOG_RESET
> #if defined(CONFIG_HARD_I2C) || defined(CONFIG_SOFT_I2C)
>     init_func_i2c,
> #endif
> 
> and init_fdt() calls fdt_open_into().

RAM is _not_ available at that stage.

>> Using the FDT directly from ROM is not recommended because access 
>> might be slow, but we likely need it for early initialization.
> 
> I don't access speed is important for the reading the FDT, especially 
> flash vs. RAM.  It's not that much slower.

Depends, you might be right for FLASH on a 32-bit bus. On slow ROM 
devices and slow processors, it matters.

Wolfgang.

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Timur Tabi]

Wolfgang Grandegger wrote:

> But you need it anyhow in RAM for booting Linux. Why not doing it early, 
> e.g. after relocation when memory is available.

Ok.

>> So the question is: do we want U-Boot to use this node to determine 
>> how much RAM there is, or do we want U-Boot to determine how much RAM 
>> there is and update this node?
> 
> Both makes sense, I think. 

Well, we can't do both.  We have to do one or the other.  I think we should have U-Boot 
determine the amount of RAM and update the device tree accordingly.

> How we finally use FDT it U-Boot is not yet 
> clear, but exhaustive usage like in the kernel seems not attractive to 
> me. Currently I just need it do enable some devices dynamically, like 
> PCMCIA, RTC and CAN and configure the LCD controller for various panels.

Once we let the cat out of the bag, there's no telling what people will do.  My guess is 
that we will probably never reach the kernel's level of usage, but we'll just keep getting 
closer and closer.
> Don't like the "don't care" argument. If you can make your code faster, 
> just do it.

I'm okay with waiting until RAM is enabled and then copying the device tree into RAM 
before using it.  But again, that assumes that CFG_FDT_ADDR_RAM is defined.

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Grandegger]

Timur Tabi wrote:
> Wolfgang Grandegger wrote:
> 
>> RAM is _not_ available at that stage.
> 
> Do we really need RAM to parse the device tree and configure U-Boot?  I 
> think not.

But you need it anyhow in RAM for booting Linux. Why not doing it early, 
e.g. after relocation when memory is available.

> The device tree has a memory section:
> 
>     memory {
>         device_type = "memory";
>         reg = <00000000 10000000>;    // 256MB
>     };
> 
> So the question is: do we want U-Boot to use this node to determine how 
> much RAM there is, or do we want U-Boot to determine how much RAM there 
> is and update this node?

Both makes sense, I think. How we finally use FDT it U-Boot is not yet 
clear, but exhaustive usage like in the kernel seems not attractive to 
me. Currently I just need it do enable some devices dynamically, like 
PCMCIA, RTC and CAN and configure the LCD controller for various panels.

>> Depends, you might be right for FLASH on a 32-bit bus. On slow ROM 
>> devices and slow processors, it matters.
> 
> I still don't see how it's important.  If the device tree is on slow 
> memory, so what?  You have to read it sooner or later.  If your board 
> can't handle this feature, then don't enable it, and configure U-Boot 
> the "old fashioned way".

Don't like the "don't care" argument. If you can make your code faster, 
just do it.

Wolfgang.

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Jerry Van Baren]

Timur Tabi wrote:
> Wolfgang Grandegger wrote:
> 
>> - In the early boot phase, before relocation, the FDT is checked and an
>>   error message printed in case it's not found or invalid: 
>>
>>      CPU:  MPC5200 v1.0, Core v1.1 at 396 MHz
>>            Bus 132 MHz, IPB 66 MHz, PCI 33 MHz
>>      FDT:  FDT_ERR_BADMAGIC (or OK, or version number?)
>>
>>     At this level also the compatibility of the FDT tree could be checked
>>     using fdt_boardcheck().
> 
> I think fdt_checkboard() (or boardcheck) should be run from inside the 
> fdt_open_into() command.  This takes advantage of the existing mechanism 
> of fdt_open_into() to return an error.  It also allows for a device tree 
> to be opened after U-Boot has booted.

NO.  fdt_open_into() is part of libfdt, which is a _generic_ fdt 
library.  fdt_check_board() would be board specific and any call-out to 
it from the generic libfdt would be a mistake because it would make 
libfdt u-boot specific.

If we implement a fdt_checkboard(), I agree with Wolfgang that it would 
be called early in the board-specific start up code.

If we implement a fdt_checkboard(), I would create a new subcommand for 
it.  While it could be added to the "fdt addr" command to verify the 
user pointed to a valid fdt, I would strongly resist that.  "UNIX was 
not designed to stop its users from doing stupid things, as that would 
also stop them from doing clever things." ? Doug Gwyn
   <http://en.wikipedia.org/wiki/Unix_philosophy#Quotes>

The above quote is another reason for my shouting "NO" above.

>> - After relocation, the blob is copied into memory via fdt_open_into()
>>    to a defined place and "fdt" is updated accordingly. 
> 
> So we'll need to have CFG_FDT_ADDR_FLASH and CFG_FDT_ADDR_RAM.
> 
>> Not sure, what
>>    location in RAM to use, but it should fit into the existing scheme.
>>    Any recommendations?
>>
>> - When U-Boot is up, "fdt" points to a valid FDT, e.g. "fdt addr" is not
>>    necessary.
> 
> I think this feature needs to be optional.  That is, if CFG_FDT_ADDR_xxx 
> are defined, then we can enable this feature.  Otherwise, fdt_addr will 
> still be necessary.  Remember, we'll still need to support architectures 
> that don't have device trees.

"fdt addr" (no underscore) is the subcommand that allows the user to 
change the fdt address (implementation: it sets the C variable "fdt"). 
I would be reluctant to remove the "addr" subcommand because the 
user/scripts may want to change which fdt is used.  Given Wolfgang's 
thoughts/proposals above, it will not be used very often, but it would 
still be useful for developers.

"fdt addr" would also be more useful if "fdt addr" printed out the 
current value of the variable "fdt" (I don't believe it is implemented 
this way currently).

Best regards,
gvb

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Timur Tabi]

Jerry Van Baren wrote:

> NO.  fdt_open_into() is part of libfdt, which is a _generic_ fdt 
> library.  fdt_check_board() would be board specific and any call-out to 
> it from the generic libfdt would be a mistake because it would make 
> libfdt u-boot specific.

I can understand that, but then we have a problem.  We don't want to be able to use a 
device tree without checking it.  We have to implement some kind of mechanism to ensure 
that fdt_checkboard() is called before the kernel is booted.

> If we implement a fdt_checkboard(), I agree with Wolfgang that it would 
> be called early in the board-specific start up code.

But *after* fdt_open_into() is called.  Perhaps we need a higher-level version of 
fdt_open_into()?  And perhaps "fdt addr" should call this function instead?

> If we implement a fdt_checkboard(), I would create a new subcommand for 
> it.  While it could be added to the "fdt addr" command to verify the 
> user pointed to a valid fdt, I would strongly resist that.  

Ok.

 > "UNIX was
> not designed to stop its users from doing stupid things, as that would 
> also stop them from doing clever things." ? Doug Gwyn

U-Boot isn't Unix.

> "fdt addr" (no underscore) is the subcommand that allows the user to 
> change the fdt address

*change* the fdt address?  I'm not sure that's the best way of handling it.  The fdt 
library should simply be told where the FDT is located.  Moving the FDT around in memory 
is probably beyond its scope.

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Jerry Van Baren]

Timur Tabi wrote:
> Jerry Van Baren wrote:

[snip]

>  > "UNIX was
>> not designed to stop its users from doing stupid things, as that would 
>> also stop them from doing clever things." ? Doug Gwyn
> 
> U-Boot isn't Unix.

Indeed.  However, the above quote is one of Wolfgang Denk's favorites. 
Don't diss it, Wolfgang will get p1ssed.  ;-)

>> "fdt addr" (no underscore) is the subcommand that allows the user to 
>> change the fdt address
> 
> *change* the fdt address?  I'm not sure that's the best way of handling 
> it.  The fdt library should simply be told where the FDT is located.  
> Moving the FDT around in memory is probably beyond its scope.

Yes, that is what "fdt addr" does today, it tells the u-boot innards 
where the blob is (sets/changes the blob location).  The user can 
download a new blob and switch to using it via the "fdt addr" command.

Your statment "The fdt library should simply be told where the FDT is 
located." doesn't have meaning in this context:
1) We are talking about the user command "fdt", not the C code that
      implements the use and manipulation of flattened device trees
2) All of the libfdt functions take the blob address as the first
      parameter so your statement is accurate already.

The user can use the "fdt addr" command to set/change the location of 
the blob.  Moving blobs is not out of scope, it is what "fdt move" does. 
  It's all in there and useful.

I think you are confusing the "fdt" command (with lots of subcommands) 
with the C code implementation.

Best regards,
gvb

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Timur Tabi]

Jerry Van Baren wrote:

> Yes, that is what "fdt addr" does today, it tells the u-boot innards 
> where the blob is (sets/changes the blob location).  The user can 
> download a new blob and switch to using it via the "fdt addr" command.

By "change", I thought you meant that "fdt addr" would actually move the device tree, 
since that's technically changing the address.  Perhaps you meant "set the address"?

> The user can use the "fdt addr" command to set/change the location of 
> the blob.  Moving blobs is not out of scope, it is what "fdt move" does. 

How is "fdt move" different than cp.b followed by another "fdt addr"?

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Jerry Van Baren]

Timur Tabi wrote:
> Jerry Van Baren wrote:
> 
>> Yes, that is what "fdt addr" does today, it tells the u-boot innards 
>> where the blob is (sets/changes the blob location).  The user can 
>> download a new blob and switch to using it via the "fdt addr" command.
> 
> By "change", I thought you meant that "fdt addr" would actually move the 
> device tree, since that's technically changing the address.  Perhaps you 
> meant "set the address"?

Yes.

>> The user can use the "fdt addr" command to set/change the location of 
>> the blob.  Moving blobs is not out of scope, it is what "fdt move" does. 
> 
> How is "fdt move" different than cp.b followed by another "fdt addr"?

Conceptually the same thing but easier: you don't have to know (guess) 
the blob size because fdt_open_into() gets the size from the source blob.

gvb

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Denk]

In message <464DBFC8.4050708@freescale.com> you wrote:
>
> So the question is: do we want U-Boot to use this node to determine how much RAM there is, 
> or do we want U-Boot to determine how much RAM there is and update this node?

Tradition is that U-Boot will determine how much RAM there is, and  I
definitely  want  to  keep it that way. Among other things, this is a
cheap and yet still pretty efficient protection against most types of
RAM errors.

> I still don't see how it's important.  If the device tree is on slow memory, so what?  You 

Timu, there is lots of code in U-Boot that you haven't seen yet...

> have to read it sooner or later.  If your board can't handle this feature, then don't 
> enable it, and configure U-Boot the "old fashioned way".

Having  to  read  it  later  (after  relocation  into  RAM)  may   be
*significantly*  faster. We can then use buffering, while we may have
to use repeated small reads (repeated for each element we're  looking
up)  while  running from ROM. Remember that there is more things than
just NOR flash. Data may be stored in slow serial devices like EEPROM
on I2C, or serial flash on SPI, or NAND flash, etc.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
"The first rule of magic is simple. Don't waste your time waving your
hands and hoping when a rock or a club will do."
                                               - McCloctnik the Lucid

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Denk]

In message <464DC7D8.2050703@freescale.com> you wrote:
>
>  > "UNIX was
> > not designed to stop its users from doing stupid things, as that would
> > also stop them from doing clever things." Doug Gwyn
> 
> U-Boot isn't Unix.

But is very closely  follows  the  Unix  design  philosophy.  If  you
haven't  understood  this  by  now, you should try to forget what you
know about U-Boot, and restart from scratch.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
There are very few personal problems that cannot be solved through  a
suitable application of high explosives.

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Denk]

In message <464DCEAE.3030201@smiths-aerospace.com> you wrote:
>
> Indeed.  However, the above quote is one of Wolfgang Denk's favorites.

Indeed it is.

> Don't diss it, Wolfgang will get p1ssed.  ;-)

Not really. Everybody has the right to have his own opinion. As  long
as they not try to code such opinions into U-Boot, that is ;-)

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
Tactical? TACTICAL!?!? Hey, buddy, we went from kilotons to  megatons
several  minutes  ago.  We don't need no stinkin' tactical nukes. (By
the way, do you have change for 10 million people?)           - lwall

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Jon Loeliger]

On Fri, 2007-05-18 at 14:16, Wolfgang Denk wrote:

> > Don't diss it, Wolfgang will get p1ssed.  ;-)
> 
> Not really. Everybody has the right to have his own opinion. As  long
> as they not try to code such opinions into U-Boot, that is ;-)

Or, to paraphrase Wolfgang here:

     Everyone else is entitled to their own wrong opinion.

:-)

jdl

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Grandegger]

Jerry Van Baren wrote:
> Timur Tabi wrote:
>> Jerry Van Baren wrote:
>>
>>> Yes, that is what "fdt addr" does today, it tells the u-boot innards 
>>> where the blob is (sets/changes the blob location).  The user can 
>>> download a new blob and switch to using it via the "fdt addr" command.
>>
>> By "change", I thought you meant that "fdt addr" would actually move 
>> the device tree, since that's technically changing the address.  
>> Perhaps you meant "set the address"?
> 
> Yes.
> 
>>> The user can use the "fdt addr" command to set/change the location of 
>>> the blob.  Moving blobs is not out of scope, it is what "fdt move" does. 
>>
>> How is "fdt move" different than cp.b followed by another "fdt addr"?
> 
> Conceptually the same thing but easier: you don't have to know (guess) 
> the blob size because fdt_open_into() gets the size from the source blob.

Summing up, brainstorming a bit more, here are my revised ideas:

The following definitions control the FDT usage in U-Boot:

CFG_FDT_ADDR_FLASH:
	If defined, "fdt" is set to that address at compile time. The
         FDT can be used from the early beginning of the boot.

CFG_FDT_ADDR_BY_ENV:
	If defined, the env variable "fdtaddr" is looked up early in the
         boot and "fdt" is set accordingly. This allows to hold more than
         one blob in FLASH and select one via env setting. This would
         allow for _one_ combination of images of U-Boot + Linux + Blobs
         for a _set_ of boards.

CFG_FDT_ADDR_RAM:
	If defined, the blob is moved to RAM after relocation for
         further preparation or for performance reasons. "fdt" is re-set
         accordingly. The blob is then ready and in place for booting
         Linux. If CFG_FDT_ADDR_RAM is set to 0, the blob will be copied
	to a default location, e.g. before the initrd location.

A board-specific checkboad function is called as early as possible to 
verify the FDT.

This should also make Timur happy, as he has the choice, e.g. read the 
FDT solely from FLASH. With this scheme, I also do not see the real need 
for fdt commands to manipulate the blob in RAM. Read-only support would 
be a nice to have for debugging, though.

Please comment.

Wolfgang.

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Denk]

In message <46500875.6060706@grandegger.com> you wrote:
>
> CFG_FDT_ADDR_FLASH:
> 	If defined, "fdt" is set to that address at compile time. The
>          FDT can be used from the early beginning of the boot.

Just nitpicking: maybe we should  call  this  CFG_FDT_ADDR_STATIC  or
CFG_FDT_ADDR_DEFAULT  or  CFG_FDT_ADDR_INIT  or  something like that.
Rationale: flash is just one of the  possible  storage  devies  -  it
could be ROM instead, or even RAM in certain configurations.

Also, while we are defining this, please keep in mind that sooner or
later someone will come up with the idea of storing the FDT in EEPROM,
so we might want to reserve such identifiers.

> CFG_FDT_ADDR_BY_ENV:
> 	If defined, the env variable "fdtaddr" is looked up early in the
>          boot and "fdt" is set accordingly. This allows to hold more than
>          one blob in FLASH and select one via env setting. This would
>          allow for _one_ combination of images of U-Boot + Linux + Blobs
>          for a _set_ of boards.

Traditionally, that should be named CFG_FDT_ADDR_IN_ENV

> CFG_FDT_ADDR_RAM:
> 	If defined, the blob is moved to RAM after relocation for
>          further preparation or for performance reasons. "fdt" is re-set
>          accordingly. The blob is then ready and in place for booting
>          Linux. If CFG_FDT_ADDR_RAM is set to 0, the blob will be copied
> 	to a default location, e.g. before the initrd location.

I'm not sure I understand  this  -  will  CFG_FDT_ADDR_RAM  hold  the
*address*  in  RAM  where  the FDT gets copied to? That sounds pretty
static to me.

> A board-specific checkboad function is called as early as possible to 
> verify the FDT.

"checkboard()" is a name that can mean anything. If the  function  is
to  check  or  to  verify the FDT, the function name should represent
this, i. e. please  callit  checkfdt()  or  verifyfdt()  of  probably
fdtcheck() / fdtverify() or fdt_check() / fdt_verify().


Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
The night sky over the planet Krikkit is the least interesting  sight
in the entire Universe.
                 - Douglas Adams _Life, the Universe, and Everything_

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Jerry Van Baren]

Wolfgang Denk wrote:
> In message <46500875.6060706@grandegger.com> you wrote:
>> CFG_FDT_ADDR_FLASH:
>> 	If defined, "fdt" is set to that address at compile time. The
>>          FDT can be used from the early beginning of the boot.
> 
> Just nitpicking: maybe we should  call  this  CFG_FDT_ADDR_STATIC  or
> CFG_FDT_ADDR_DEFAULT  or  CFG_FDT_ADDR_INIT  or  something like that.
> Rationale: flash is just one of the  possible  storage  devies  -  it
> could be ROM instead, or even RAM in certain configurations.
> 
> Also, while we are defining this, please keep in mind that sooner or
> later someone will come up with the idea of storing the FDT in EEPROM,
> so we might want to reserve such identifiers.

Good points, I agree with them.  One possibility would be to name it 
CFG_FDT_ADDR_INIT (my 2c for name choice) and #define it to a static 
address for the typical flash storage case and #define it to be a 
function that returns an address for the read-from-EEPROM case.

>> CFG_FDT_ADDR_BY_ENV:
>> 	If defined, the env variable "fdtaddr" is looked up early in the
>>          boot and "fdt" is set accordingly. This allows to hold more than
>>          one blob in FLASH and select one via env setting. This would
>>          allow for _one_ combination of images of U-Boot + Linux + Blobs
>>          for a _set_ of boards.
> 
> Traditionally, that should be named CFG_FDT_ADDR_IN_ENV

Ditto.

>> CFG_FDT_ADDR_RAM:
>> 	If defined, the blob is moved to RAM after relocation for
>>          further preparation or for performance reasons. "fdt" is re-set
>>          accordingly. The blob is then ready and in place for booting
>>          Linux. If CFG_FDT_ADDR_RAM is set to 0, the blob will be copied
>> 	to a default location, e.g. before the initrd location.
> 
> I'm not sure I understand  this  -  will  CFG_FDT_ADDR_RAM  hold  the
> *address*  in  RAM  where  the FDT gets copied to? That sounds pretty
> static to me.

This would be used if the blob has to be copied out of flash into RAM 
(or could be part of the read-from-EEPROM usage).

I'm not sure this is necessary (echoing wd's "pretty static" reaction). 
  The board-specific code in the start up should know where a good place 
to place the RAM copy of the blob is, for instance, right after the RAM 
copy of u-boot.  Is there a case where it _must_ be a fixed address?  I 
cannot think of any.

If there is a case where it _must_ be fixed, it seems to me it would be 
so unusual a case that I would leave it up to the board supporter to 
hardcode it in the board-specific start up.

My gut feel is to not document/define a CFG_FDT_ADDR_RAM until we get 
use cases that show that it is a Good Thing[tm].

>> A board-specific checkboad function is called as early as possible to 
>> verify the FDT.
> 
> "checkboard()" is a name that can mean anything. If the  function  is
> to  check  or  to  verify the FDT, the function name should represent
> this, i. e. please  callit  checkfdt()  or  verifyfdt()  of  probably
> fdtcheck() / fdtverify() or fdt_check() / fdt_verify().

I'm somewhat skeptical about the fdt_checkboard() concept, how well it 
would work in practice.  If the blob is for the wrong board, will the 
serial work?  Sometimes yes, sometimes no.  For the times the answer is 
"yes", the ability is probably worth considering, at least.

I would like to see the verification/validation that we currently do on 
the env data to be done on the blob as well.  This is heading towards my 
assertion that the blob can take over most, perhaps all, of the duties 
of the current "env" storage.  Not all of the thoughts below are 
directly on topic since I'm expanding beyond just u-boot config.
* A CRC
* Backup copy (if selected in the board config)
* Default compiled in copy (?)
   * Likely not useful since, by definition, some parts of the fdt would
       be board specific and not detectable by the board start up code.
   * Hmm, if we had a minimal default compiled in copy, we could compare
       its values to a user-loadable version as (part of) a
       fdt_checkboard() function.

> Best regards,
> Wolfgang Denk

Ditto,
gvb

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Grandegger]

Wolfgang Denk wrote:
> In message <46500875.6060706@grandegger.com> you wrote:
>> CFG_FDT_ADDR_FLASH:
>> 	If defined, "fdt" is set to that address at compile time. The
>>          FDT can be used from the early beginning of the boot.
> 
> Just nitpicking: maybe we should  call  this  CFG_FDT_ADDR_STATIC  or
> CFG_FDT_ADDR_DEFAULT  or  CFG_FDT_ADDR_INIT  or  something like that.
> Rationale: flash is just one of the  possible  storage  devies  -  it
> could be ROM instead, or even RAM in certain configurations.
> 
> Also, while we are defining this, please keep in mind that sooner or
> later someone will come up with the idea of storing the FDT in EEPROM,
> so we might want to reserve such identifiers.

Then something similar to the ENV could be chosen:

   CFG_FDT_ADDR
   CFG_FDT_IS_IN_FLASH
   CFG_FDT_IS_IN_xxx
   ...

>> CFG_FDT_ADDR_BY_ENV:
>> 	If defined, the env variable "fdtaddr" is looked up early in the
>>          boot and "fdt" is set accordingly. This allows to hold more than
>>          one blob in FLASH and select one via env setting. This would
>>          allow for _one_ combination of images of U-Boot + Linux + Blobs
>>          for a _set_ of boards.
> 
> Traditionally, that should be named CFG_FDT_ADDR_IN_ENV

OK for me.

>> CFG_FDT_ADDR_RAM:
>> 	If defined, the blob is moved to RAM after relocation for
>>          further preparation or for performance reasons. "fdt" is re-set
>>          accordingly. The blob is then ready and in place for booting
>>          Linux. If CFG_FDT_ADDR_RAM is set to 0, the blob will be copied
>> 	to a default location, e.g. before the initrd location.
> 
> I'm not sure I understand  this  -  will  CFG_FDT_ADDR_RAM  hold  the
> *address*  in  RAM  where  the FDT gets copied to? That sounds pretty
> static to me.

Well, yes, this address must be suitable for Linux and should be treated 
similar to the initial ramdisk. Therefore a proper default address seems 
sufficient.

>> A board-specific checkboad function is called as early as possible to 
>> verify the FDT.
> 
> "checkboard()" is a name that can mean anything. If the  function  is
> to  check  or  to  verify the FDT, the function name should represent
> this, i. e. please  callit  checkfdt()  or  verifyfdt()  of  probably
> fdtcheck() / fdtverify() or fdt_check() / fdt_verify().

Then checkfdt(). In principle, this could be done in the already 
existing board-specific checkboard function, but a dedicated function 
for verifying the FDT makes sense, I think.

Wolfgang.

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Timur Tabi]

Wolfgang Grandegger wrote:

> Then something similar to the ENV could be chosen:
> 
>   CFG_FDT_ADDR
>   CFG_FDT_IS_IN_FLASH
>   CFG_FDT_IS_IN_xxx

We need two addresses:

1) The address where the FDT is stored when the system is powered up
2) The address in RAM where the FDT should be placed before Linux is booted.

Therefore, we can't have just CFG_FDT_ADDR.  We need CFG_FDT_ADDR_xxxx

My vote is to have xxxx be the type of memory.  So if CFG_FDT_ADDR_FLASH is defined to 
value X, that means that the FDT is stored in flash at address X.  If CFG_FDT_ADDR_EEPROM 
is defined instead, then it means that FDT is located in EEPROM at address X.

This would eliminate the "CFG_FDT_IS_IN_xxx"-type macros, which I think are redundant.

>>> CFG_FDT_ADDR_BY_ENV:
>>>     If defined, the env variable "fdtaddr" is looked up early in the
>>>          boot and "fdt" is set accordingly. This allows to hold more 
>>> than

I would rather that the FDT subsystem *set* the fdtaddr variable, instead of the other way 
around.

>>> CFG_FDT_ADDR_RAM:
>>>     If defined, the blob is moved to RAM after relocation for
>>>          further preparation or for performance reasons. "fdt" is re-set
>>>          accordingly. The blob is then ready and in place for booting
>>>          Linux. If CFG_FDT_ADDR_RAM is set to 0, the blob will be copied
>>>     to a default location, e.g. before the initrd location.

I think we're going to have to always relocate the FDT to RAM.  Considering the level of 
functionality that libfdt provides, and considering how much of that functionality depends 
on being able to write to the FDT, it makes sense to require it to be in RAM.

>> "checkboard()" is a name that can mean anything. If the  function  is

The purpose of the function is to provide board-specific code that validates the FDT.  The 
amount of checking performed is at the discretion of the function.

For example, checkboard() *should* compare the values in the board header file with the 
FDT to verify that the memory mappings map, for instance.

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Timur Tabi]

Wolfgang Grandegger wrote:
> Jerry Van Baren wrote:
>> Timur Tabi wrote:
>>> Jerry Van Baren wrote:
>>>
>>>> Yes, that is what "fdt addr" does today, it tells the u-boot innards 
>>>> where the blob is (sets/changes the blob location).  The user can 
>>>> download a new blob and switch to using it via the "fdt addr" command.
>>>
>>> By "change", I thought you meant that "fdt addr" would actually move 
>>> the device tree, since that's technically changing the address.  
>>> Perhaps you meant "set the address"?
>>
>> Yes.
>>
>>>> The user can use the "fdt addr" command to set/change the location 
>>>> of the blob.  Moving blobs is not out of scope, it is what "fdt 
>>>> move" does. 
>>>
>>> How is "fdt move" different than cp.b followed by another "fdt addr"?
>>
>> Conceptually the same thing but easier: you don't have to know (guess) 
>> the blob size because fdt_open_into() gets the size from the source blob.
> 
> Summing up, brainstorming a bit more, here are my revised ideas:
> 
> The following definitions control the FDT usage in U-Boot:
> 
> CFG_FDT_ADDR_FLASH:
>     If defined, "fdt" is set to that address at compile time. The
>         FDT can be used from the early beginning of the boot.
> 
> CFG_FDT_ADDR_BY_ENV:
>     If defined, the env variable "fdtaddr" is looked up early in the
>         boot and "fdt" is set accordingly. This allows to hold more than
>         one blob in FLASH and select one via env setting. This would
>         allow for _one_ combination of images of U-Boot + Linux + Blobs
>         for a _set_ of boards.

If CFG_FDT_ADDR_BY_ENV is *not* defined, should the FDT code then set that variable?

> CFG_FDT_ADDR_RAM:
>     If defined, the blob is moved to RAM after relocation for
>         further preparation or for performance reasons. "fdt" is re-set
>         accordingly. The blob is then ready and in place for booting
>         Linux. If CFG_FDT_ADDR_RAM is set to 0, the blob will be copied
>     to a default location, e.g. before the initrd location.

I think the FDT blob should *always* be copied to RAM.

> 
> A board-specific checkboad function is called as early as possible to 
> verify the FDT.
> 
> This should also make Timur happy, as he has the choice, e.g. read the 
> FDT solely from FLASH. 

I think I may have changed my mind a bit.  I'm not so much concerned about read-only FDT 
as I want to automate the process of copying it to RAM.

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Grandegger]

Timur Tabi wrote:
> Wolfgang Grandegger wrote:
> 
>> Then something similar to the ENV could be chosen:
>>
>>   CFG_FDT_ADDR
>>   CFG_FDT_IS_IN_FLASH
>>   CFG_FDT_IS_IN_xxx
> 
> We need two addresses:
> 
> 1) The address where the FDT is stored when the system is powered up

OK.

> 2) The address in RAM where the FDT should be placed before Linux is 
> booted.

This should be some kind of default address. Also be aware, that the 
blob can be within a uImage created with mkimage. Then the load address 
defined in the uImage should be used.

> Therefore, we can't have just CFG_FDT_ADDR.  We need CFG_FDT_ADDR_xxxx
> 
> My vote is to have xxxx be the type of memory.  So if CFG_FDT_ADDR_FLASH 
> is defined to value X, that means that the FDT is stored in flash at 
> address X.  If CFG_FDT_ADDR_EEPROM is defined instead, then it means 
> that FDT is located in EEPROM at address X.
> 
> This would eliminate the "CFG_FDT_IS_IN_xxx"-type macros, which I think 
> are redundant.

You might be right. The _IS_IN_ is used for the ENV, I have to check 
what the rational behind it is (if there is one at all).

> 
>>>> CFG_FDT_ADDR_BY_ENV:
>>>>     If defined, the env variable "fdtaddr" is looked up early in the
>>>>          boot and "fdt" is set accordingly. This allows to hold more 
>>>> than
> 
> I would rather that the FDT subsystem *set* the fdtaddr variable, 
> instead of the other way around.

I'm not sure if you understand the intended purpose. The address of the 
_initial_ blob could be stored in the env variable "fdtaddr" to select 
_one_ blob out of many in the FLASH.

>>>> CFG_FDT_ADDR_RAM:
>>>>     If defined, the blob is moved to RAM after relocation for
>>>>          further preparation or for performance reasons. "fdt" is 
>>>> re-set
>>>>          accordingly. The blob is then ready and in place for booting
>>>>          Linux. If CFG_FDT_ADDR_RAM is set to 0, the blob will be 
>>>> copied
>>>>     to a default location, e.g. before the initrd location.
> 
> I think we're going to have to always relocate the FDT to RAM.  
> Considering the level of functionality that libfdt provides, and 
> considering how much of that functionality depends on being able to 
> write to the FDT, it makes sense to require it to be in RAM.

Good, and for booting the FDT must be in RAM anyhow.

>>> "checkboard()" is a name that can mean anything. If the  function  is
> 
> The purpose of the function is to provide board-specific code that 
> validates the FDT.  The amount of checking performed is at the 
> discretion of the function.
> 
> For example, checkboard() *should* compare the values in the board 
> header file with the FDT to verify that the memory mappings map, for 
> instance.

I tend to leave it up to the board specific code where and how to verify 
the FDT. There are already various entry points like checkboard() or 
misc_init_r().

Wolfgang.

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Timur Tabi]

Wolfgang Grandegger wrote:
> Timur Tabi wrote:
>> Wolfgang Grandegger wrote:
>>
>>> Then something similar to the ENV could be chosen:
>>>
>>>   CFG_FDT_ADDR
>>>   CFG_FDT_IS_IN_FLASH
>>>   CFG_FDT_IS_IN_xxx
>>
>> We need two addresses:
>>
>> 1) The address where the FDT is stored when the system is powered up
> 
> OK.
> 
>> 2) The address in RAM where the FDT should be placed before Linux is 
>> booted.
> 
> This should be some kind of default address. 

Any default address is most likely board-specific.  It would be nice if U-Boot could 
determine the best address automatically when possible.

> Also be aware, that the 
> blob can be within a uImage created with mkimage. Then the load address 
> defined in the uImage should be used.

Yes.

> You might be right. The _IS_IN_ is used for the ENV, I have to check 
> what the rational behind it is (if there is one at all).

It's handy if you want to use the same macro to represent different types of addresses. 
Personally, I don't see much value in that.  I would rather that a particular macro be 
used to represent only one kind of value.  When I see CFG_FDT_ADDR_RAM, I know that the 
value is a virtual address that the CPU can dereference at any time.

> I'm not sure if you understand the intended purpose. The address of the 
> _initial_ blob could be stored in the env variable "fdtaddr" to select 
> _one_ blob out of many in the FLASH.

Hmm....

I can see value in that, but then that variable can contain completely different addresses 
depending on the type of storage, which I don't like.  Plus, I would rather that we use 
macro commands to set the FDT address, rather than an environment variable.  This gives us 
more flexibility.

> I tend to leave it up to the board specific code where and how to verify 
> the FDT. 

fdt_checkboard() *is* board-specific code.

There are already various entry points like checkboard() or
> misc_init_r().

But this functions don't normally know where the FDT is.  fdt_checkboard() would be 
designed specifically to validate an FDT from a board-specific point-of-view.  It's good 
to have that code isolated from other board-specific code.

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Grandegger]

Timur Tabi wrote:
> Wolfgang Grandegger wrote:
>> Jerry Van Baren wrote:
>>> Timur Tabi wrote:
>>>> Jerry Van Baren wrote:
>>>>
>>>>> Yes, that is what "fdt addr" does today, it tells the u-boot innards 
>>>>> where the blob is (sets/changes the blob location).  The user can 
>>>>> download a new blob and switch to using it via the "fdt addr" command.
>>>> By "change", I thought you meant that "fdt addr" would actually move 
>>>> the device tree, since that's technically changing the address.  
>>>> Perhaps you meant "set the address"?
>>> Yes.
>>>
>>>>> The user can use the "fdt addr" command to set/change the location 
>>>>> of the blob.  Moving blobs is not out of scope, it is what "fdt 
>>>>> move" does. 
>>>> How is "fdt move" different than cp.b followed by another "fdt addr"?
>>> Conceptually the same thing but easier: you don't have to know (guess) 
>>> the blob size because fdt_open_into() gets the size from the source blob.
>> Summing up, brainstorming a bit more, here are my revised ideas:
>>
>> The following definitions control the FDT usage in U-Boot:
>>
>> CFG_FDT_ADDR_FLASH:
>>     If defined, "fdt" is set to that address at compile time. The
>>         FDT can be used from the early beginning of the boot.
>>
>> CFG_FDT_ADDR_BY_ENV:
>>     If defined, the env variable "fdtaddr" is looked up early in the
>>         boot and "fdt" is set accordingly. This allows to hold more than
>>         one blob in FLASH and select one via env setting. This would
>>         allow for _one_ combination of images of U-Boot + Linux + Blobs
>>         for a _set_ of boards.
> 
> If CFG_FDT_ADDR_BY_ENV is *not* defined, should the FDT code then set that variable?

Yes, then the address is set to CFG_FDT_ADDR_XXX at compile time.

>> CFG_FDT_ADDR_RAM:
>>     If defined, the blob is moved to RAM after relocation for
>>         further preparation or for performance reasons. "fdt" is re-set
>>         accordingly. The blob is then ready and in place for booting
>>         Linux. If CFG_FDT_ADDR_RAM is set to 0, the blob will be copied
>>     to a default location, e.g. before the initrd location.
> 
> I think the FDT blob should *always* be copied to RAM.
> 
>> A board-specific checkboad function is called as early as possible to 
>> verify the FDT.
>>
>> This should also make Timur happy, as he has the choice, e.g. read the 
>> FDT solely from FLASH. 
> 
> I think I may have changed my mind a bit.  I'm not so much concerned about read-only FDT 
> as I want to automate the process of copying it to RAM.

As a result of discussion, in the meantime I have now also a better idea 
on how to implement FDT for U-Boot configuration. Going to make a demo 
for my Icecube board a.s.a.p.

Wolfgang.

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Jerry Van Baren]

Timur Tabi wrote:
> Wolfgang Grandegger wrote:
>> Timur Tabi wrote:
>>> Wolfgang Grandegger wrote:
>>>
>>>> Then something similar to the ENV could be chosen:
>>>>
>>>>   CFG_FDT_ADDR
>>>>   CFG_FDT_IS_IN_FLASH
>>>>   CFG_FDT_IS_IN_xxx
>>>
>>> We need two addresses:
>>>
>>> 1) The address where the FDT is stored when the system is powered up
>>
>> OK.
>>
>>> 2) The address in RAM where the FDT should be placed before Linux is 
>>> booted.
>>
>> This should be some kind of default address. 
> 
> Any default address is most likely board-specific.  It would be nice if 
> U-Boot could determine the best address automatically when possible.
> 
>> Also be aware, that the blob can be within a uImage created with 
>> mkimage. Then the load address defined in the uImage should be used.
> 
> Yes.
> 
>> You might be right. The _IS_IN_ is used for the ENV, I have to check 
>> what the rational behind it is (if there is one at all).
> 
> It's handy if you want to use the same macro to represent different 
> types of addresses. Personally, I don't see much value in that.  I would 
> rather that a particular macro be used to represent only one kind of 
> value.  When I see CFG_FDT_ADDR_RAM, I know that the value is a virtual 
> address that the CPU can dereference at any time.
> 
>> I'm not sure if you understand the intended purpose. The address of 
>> the _initial_ blob could be stored in the env variable "fdtaddr" to 
>> select _one_ blob out of many in the FLASH.
> 
> Hmm....
> 
> I can see value in that, but then that variable can contain completely 
> different addresses depending on the type of storage, which I don't 
> like.  Plus, I would rather that we use macro commands to set the FDT 
> address, rather than an environment variable.  This gives us more 
> flexibility.

Hi Timur,

You totally lost me on that assertion.  What do you mean when you say 
"macro commands?"

If you are talking preprocessor #define macros, you are comparing a 
hardcoded address (after compilation) to a runtime modifiable address in 
an env variable.

If you mean a hush script when you say "macro commands", that would be a 
way of setting an env variable, so how is that more flexible?  We 
already have the "fdt addr" command at the hush level that can be used 
by hand or in scripts to set the fdt blob address, but that is _way_ 
later in the boot cycle than what Wolfgang will be using.

[snip]

Best regards,
gvb

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Grandegger]

Timur Tabi wrote:
> Wolfgang Grandegger wrote:
>> Timur Tabi wrote:
>>> Wolfgang Grandegger wrote:
>>>
>>>> Then something similar to the ENV could be chosen:
>>>>
>>>>   CFG_FDT_ADDR
>>>>   CFG_FDT_IS_IN_FLASH
>>>>   CFG_FDT_IS_IN_xxx
>>>
>>> We need two addresses:
>>>
>>> 1) The address where the FDT is stored when the system is powered up
>>
>> OK.
>>
>>> 2) The address in RAM where the FDT should be placed before Linux is 
>>> booted.
>>
>> This should be some kind of default address. 
> 
> Any default address is most likely board-specific.  It would be nice if 
> U-Boot could determine the best address automatically when possible.
> 
>> Also be aware, that the blob can be within a uImage created with 
>> mkimage. Then the load address defined in the uImage should be used.
> 
> Yes.
> 
>> You might be right. The _IS_IN_ is used for the ENV, I have to check 
>> what the rational behind it is (if there is one at all).
> 
> It's handy if you want to use the same macro to represent different 
> types of addresses. Personally, I don't see much value in that.  I would 
> rather that a particular macro be used to represent only one kind of 
> value.  When I see CFG_FDT_ADDR_RAM, I know that the value is a virtual 
> address that the CPU can dereference at any time.
> 
>> I'm not sure if you understand the intended purpose. The address of 
>> the _initial_ blob could be stored in the env variable "fdtaddr" to 
>> select _one_ blob out of many in the FLASH.
> 
> Hmm....
> 
> I can see value in that, but then that variable can contain completely 
> different addresses depending on the type of storage, which I don't 
> like.  Plus, I would rather that we use macro commands to set the FDT 
> address, rather than an environment variable.  This gives us more 
> flexibility.

What do you mean with "macro commands"? Simply macro definitions in the 
board's config file? Such an address is fixed at compile time pointing 
to one FDT blob. The purpose of the env variable "fdtaddr" is to select 
that address at run time. Again, this allows to hold more than one blob 
in FLASH and select one via env setting. This would allow for _one_ 
combination of images of U-Boot + Linux + Blobs for a _set_ of boards 
which might reduce the effort to bring up board. Nevertheless, regard it 
as useful add-on.

>> I tend to leave it up to the board specific code where and how to 
>> verify the FDT. 
> 
> fdt_checkboard() *is* board-specific code.
> 
> There are already various entry points like checkboard() or
>> misc_init_r().
> 
> But this functions don't normally know where the FDT is.  

They know. The global variable "fdt" will point to the blob and a very 
early common check has then already be done. Note that the FDT commands 
also uses the global "fdt" variable.

> fdt_checkboard() would be designed specifically to validate an FDT from 
> a board-specific point-of-view.  It's good to have that code isolated 
> from other board-specific code.

Why more entry points if there are already suitable ones. I'm still not 
sure if we need an extra function.

Wolfgang.

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Timur Tabi]

Jerry Van Baren wrote:

> You totally lost me on that assertion.  What do you mean when you say 
> "macro commands?"

It's a sequence of commands stored in an environment variable, executed via the "run" command.

I guess they're called hush scripts.

> If you mean a hush script when you say "macro commands", that would be a 
> way of setting an env variable, so how is that more flexible?  We 
> already have the "fdt addr" command at the hush level that can be used 
> by hand or in scripts to set the fdt blob address, but that is _way_ 
> later in the boot cycle than what Wolfgang will be using.

I mean more flexible in that you can use a hush script to set that variable and do other 
things at boot time.

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Denk]

In message <4651D0B9.9080000@freescale.com> you wrote:
>
> depending on the type of storage, which I don't like.  Plus, I would rather that we use 
> macro commands to set the FDT address, rather than an environment variable.  This gives us 
> more flexibility.

Please explain. I don't understand what you mean or which restrictions
you see.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
It would be illogical to assume that all conditions remain stable
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[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Wolfgang Denk]

In message <4651E579.40905@freescale.com> you wrote:
>
> > You totally lost me on that assertion.  What do you mean when you say 
> > "macro commands?"
> 
> It's a sequence of commands stored in an environment variable, executed via the "run" command.

That does not win you  anything  over  just  setting  an  environment
variable - you can maniopulate this later as you like anyway.

> I guess they're called hush scripts.

No. Hush (shell) scripts are  executed  by  the  hush  shell;  simple
command  /  variable  substitution  is also available with the simple
command line parser.

> I mean more flexible in that you can use a hush script to set that variable and do other 
> things at boot time.

This is most probably much too late for the things needed -  you  can
do  such  things only after relocation to RAM, while WolfgangG. needs
access very early.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
PLEASE NOTE: Some Quantum Physics Theories Suggest That When the Con-
sumer Is Not Directly Observing This Product, It May Cease  to  Exist
or Will Exist Only in a Vague and Undetermined State.

[U-Boot-Users] Ideas on U-Boot configuration with FDT

[Timur Tabi]

Wolfgang Denk wrote:
> In message <4651D0B9.9080000@freescale.com> you wrote:
>> depending on the type of storage, which I don't like.  Plus, I would rather that we use 
>> macro commands to set the FDT address, rather than an environment variable.  This gives us 
>> more flexibility.
> 
> Please explain. I don't understand what you mean or which restrictions
> you see.

By "macro command", I meant "hush script".  And by more flexibility, I meant that instead 
of using one environment variable to specify which FDT to use (a situation that really 
shouldn't occur, and will probably never occur once we we have dynamic FDTs in place), 
just have the user run a different hush script to set the fdt address.

However, now that I think about it, I'm not sure what my point is any more.

-- 
Timur Tabi
Linux Kernel Developer @ Freescale