[U-Boot] [PATCH v4 6/6] common: Generic loader for file system

[Chee, Tien Fong <tien.fong.chee@intel.com>]

On Mon, 2018-07-30 at 10:05 -0600, Simon Glass wrote:
> Hi Michal,
> 
> On 30 July 2018 at 07:30, Michal Simek <michal.simek@xilinx.com>
> wrote:
> > 
> > On 30.7.2018 15:26, Simon Glass wrote:
> > > 
> > > Hi,
> > > 
> > > On 27 July 2018 at 02:40, Chee, Tien Fong <tien.fong.chee@intel.c
> > > om> wrote:
> > > > 
> > > > 
> > > > On Thu, 2018-07-26 at 11:03 +0200, Michal Simek wrote:
> > > > > 
> > > > > On 25.7.2018 18:03, Tom Rini wrote:
> > > > > > 
> > > > > > 
> > > > > > On Wed, Jul 25, 2018 at 09:47:17AM -0600, Simon Glass
> > > > > > wrote:
> > > > > > > 
> > > > > > > 
> > > > > > > Hi,
> > > > > > > 
> > > > > > > On 25 July 2018 at 03:48, Michal Simek <michal.simek@xili
> > > > > > > nx.com>
> > > > > > > wrote:
> > > > > > > > 
> > > > > > > > 
> > > > > > > > 
> > > > > > > > On 25.7.2018 08:31, Chee, Tien Fong wrote:
> > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > On Wed, 2018-07-18 at 16:48 +0200, Michal Simek
> > > > > > > > > wrote:
> > > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > > > On 6.7.2018 10:28, tien.fong.chee at intel.com wrote:
> > > > > > > > > > > 
> > > > > > > > > > > 
> > > > > > > > > > > 
> > > > > > > > > > > From: Tien Fong Chee <tien.fong.chee@intel.com>
> > > > > > > > > > > 
> > > > > > > [...]
> > > > > > > 
> > > > > > > > 
> > > > > > > > 
> > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > > > Also that DT binding is quite weird and I don't
> > > > > > > > > > think you
> > > > > > > > > > will get
> > > > > > > > > > ACK
> > > > > > > > > > for this from device tree community at all. I think
> > > > > > > > > > that
> > > > > > > > > > calling via
> > > > > > > > > > platdata and avoid DT nodes would be better way to
> > > > > > > > > > go.
> > > > > > > > > Why do you think DT binding is weird? The DT is
> > > > > > > > > designed
> > > > > > > > > based on Simon
> > > > > > > > > proposal, and i believe following the rules in DTS
> > > > > > > > > spec.
> > > > > > > > > There are some DT benefits with current design, i
> > > > > > > > > think
> > > > > > > > > someone may be
> > > > > > > > > maintainer need to made the final decision on the
> > > > > > > > > design.
> > > > > > > > It is software configuration in file which should
> > > > > > > > mostly
> > > > > > > > describe
> > > > > > > > hardware and state for hardware configuration.
> > > > > > > > 
> > > > > > > > Your fs_loader node is purely describe sw configuration
> > > > > > > > which
> > > > > > > > shouldn't
> > > > > > > > be here.
> > > > > > > > You have there run time configuration via variables. I
> > > > > > > > think
> > > > > > > > using only
> > > > > > > > this way is enough. Default variables will match what
> > > > > > > > you would
> > > > > > > > want to
> > > > > > > > add to DT.
> > > > > > > I think DT makes sense in the U-Boot context.
> > > > > > > 
> > > > > > > We don't have a user space to handle policy decisions,
> > > > > > > and the
> > > > > > > 'chosen' node is a good place to configure these common
> > > > > > > features.
> > > > > > > 
> > > > > > > While you can argue that the partition or filesystem
> > > > > > > where an
> > > > > > > image
> > > > > > > comes from is a software config, it is something that has
> > > > > > > to be
> > > > > > > configured. It has impact on hardware too, since the FPGA
> > > > > > > has to
> > > > > > > get
> > > > > > > its firmware from somewhere. We use the chosen node to
> > > > > > > specify
> > > > > > > the
> > > > > > > UART to use, and this is no different. Again, we don't
> > > > > > > have user-
> > > > > > > space
> > > > > > > config files in U-Boot.
> > > > > > > 
> > > > > > > This argument comes up from time to time and I'd really
> > > > > > > like to
> > > > > > > put it
> > > > > > > to bed for U-Boot. I understand that Linux has its own
> > > > > > > approach
> > > > > > > and
> > > > > > > rules, but in some cases they serve U-Boot poorly.
> > > > > > I want to second this as well.  So long as we're using our
> > > > > > prefix
> > > > > > and
> > > > > > we've thought through and discussed what we're trying to do
> > > > > > here,
> > > > > > it's
> > > > > > OK to do things that might not be accepted for Linux.
> > > > > > 
> > > > > I have not a problem with using chosen node with u-boot
> > > > > prefix
> > > > > properties and my colleague hopefully with finish work about
> > > > > moving
> > > > > u-boot,dm-pre-reloc; to chosen node where it should be
> > > > > (because
> > > > > current
> > > > > solution has also problem with ordering).
> > > > > 
> > > > > In this loader case doc is saying that you can rewrite it
> > > > > with
> > > > > variables
> > > > > on the prompt (or via script).
> > > > > For cases that you want to autodetect platform and pass/load
> > > > > correct
> > > > > dtb
> > > > > which setup u-boot this can be problematic and using DT is
> > > > > could be
> > > > > considered as easier for use.
> > > > > 
> > > > > In this case this is what was proposed:
> > > > > 
> > > > > +     fs_loader0: fs-loader at 0 {
> > > > > +             u-boot,dm-pre-reloc;
> > > > > +             compatible = "u-boot,fs-loader";
> > > > > +             phandlepart = <&mmc 1>;
> > > > > +     };
> > > > > 
> > > > > +     fs_loader1: fs-loader at 1 {
> > > > > +             u-boot,dm-pre-reloc;
> > > > > +             compatible = "u-boot,fs-loader";
> > > > > +             mtdpart = "UBI",
> > > > > +             ubivol = "ubi0";
> > > > > +     };
> > > > > 
> > > > > u-boot,dm-pre-reloc; requires DM_FLAG_PRE_RELOC which is not
> > > > > setup
> > > > > for
> > > > > this driver - it means this should be here.
> > > > You are right, i missed this one. The intention of design
> > > > enables user
> > > > to call any loader with default storage through the sequence
> > > > number  if
> > > > fs loader is not defined in chosen. For example, there is a
> > > > case where
> > > > system loading the file from SDMMC, NAND and QSPI.
> > > > > 
> > > > > 
> > > > > compatible = "u-boot,fs-loader"; - bind and probe are empty
> > > > > that's
> > > > > why
> > > > > this is only used for filling platdata but driver has no user
> > > > > that's
> > > > > why
> > > > > this is unused till someone calls that functions.
> > > > > 
> > > > > phandlepart/mtdpart/ubivol is just for setup.
> > > > There are some benefits with driver model:
> > > > 1. Saving space, calling when need.
> > > > 2. Handle memory allocation and deallocation automatically.
> > > > > 
> > > > > 
> > > > > For the first case you can just use in chosen node:
> > > > > u-boot,fs-loader = <&mmc 1>;
> > > > > 
> > > > > And for UBIfs. I have never played with that but I expect it
> > > > > shouldn't
> > > > > be big problem to describe it differently too (something
> > > > > like)
> > > > > u-boot,fs-loader = <0 ubi0>;
> > > > Need consider description for UBIFS, using fs-loader seems not
> > > > working
> > > > for UBIFS, since more arguments such as mtdpartition and mtd
> > > > volume
> > > > need passing into driver. In order to avoid messing, fs_loader
> > > > can act
> > > > the pointer to the chosen.
> > > > 
> > > > Anyway, i have no strong opinion with driver designed via
> > > > platdata or
> > > > driver model if we can resolve the problem for UBIFS and
> > > > maintainers
> > > > agree with it.
> > > > > 
> > > > > 
> > > > > Then this driver/interface can stay in DT where it should
> > > > > stay. The
> > > > > only
> > > > > thing is how this should be initialized because there is no
> > > > > compatible
> > > > > string. But you can do that via platdata for platforms which
> > > > > want to
> > > > > use
> > > > > this.
> > > We should add a compatible string then :-)
> > Isn't driver name used in case of platdata initialization?
> If the node is in /chosen and has a compatible string, it will be
> bound automatically. Manually binding a device is really just a
> fallback for particular situations (e.g. buses like PCI where we
> often
> rely on probing to find out what is on the bus).
So, is this still the same with current implementation?
/ {
	chosen {
		firmware-loader = &fs_loader0;
	};

	fs_loader0: fs-loader at 0 {
		u-boot,dm-pre-reloc;
		compatible = "u-boot,fs-loader";
		source-partition = <&mmc 1>;
	};
};

> 
> Regards,
> Simon