BCM36xx support.

BCM36xx support.

[Rogier Wolff]

While working on SPI and I2C support for the BCM2835, I found the
BCM63xx SPI driver in the kernel. Turns out that this support
was partially merged: 

The support can only be enabled when BCM63xx configuration symbol
is defined which menuconfig lists as: 

 Symbol: BCM63XX [=BCM63XX]                                                
   Type  : unknown                                                           

I'd say the definition of this is not possible through the normal
channels.

And in the driver (drivers/spi/spi-bcm63xx.c) I see: 

#include <bcm63xx_dev_spi.h>

but that file is not in the current git release.

(some more googling has resulted in me finding out that I don't want
to know how the 63xx SPI controller works as it's for a MIPS processor
while the 2835 is ARM).

Roger.

-- 
** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2600998 **
**    Delftechpark 26 2628 XH  Delft, The Netherlands. KVK: 27239233    **
*-- BitWizard writes Linux device drivers for any device you may have! --*
The plan was simple, like my brother-in-law Phil. But unlike
Phil, this plan just might work.

Re: BCM36xx support.

[Florian Fainelli]

Hi Rogier,

First of all, you should have CC'd linux-mips, because that's where BCM63xx 
development happens.

On Wednesday 18 April 2012 07:51:40 Rogier Wolff wrote:
> 
> While working on SPI and I2C support for the BCM2835, I found the
> BCM63xx SPI driver in the kernel. Turns out that this support
> was partially merged: 
> 
> The support can only be enabled when BCM63xx configuration symbol
> is defined which menuconfig lists as: 
> 
>  Symbol: BCM63XX [=BCM63XX]                                                
>    Type  : unknown                                                           
> 
> I'd say the definition of this is not possible through the normal
> channels.
> 
> And in the driver (drivers/spi/spi-bcm63xx.c) I see: 
> 
> #include <bcm63xx_dev_spi.h>
> 
> but that file is not in the current git release.

No, it did not make it for a reason I ignore, probably miscommunication.

> 
> (some more googling has resulted in me finding out that I don't want
> to know how the 63xx SPI controller works as it's for a MIPS processor
> while the 2835 is ARM).

And so? if the core is the same, just use it on your platform too. If you have 
a look at the architecture files, you will see that the various BCM63xx SoC 
have their internal registers shuffled but the SPI core is always software 
compatible, another set of registers can be added for BCM2835.

I have no objection making such a driver more generic and not limited to 
bcm63xx like it is right now.
--
Florian

Re: BCM36xx support.

[Rogier Wolff]

Hi Florian, 

On Thu, May 31, 2012 at 03:55:34PM +0200, Florian Fainelli wrote:
> First of all, you should have CC'd linux-mips, because that's where
> BCM63xx development happens.

As I'm not familiar with mips-development, I didn't know that. 

> On Wednesday 18 April 2012 07:51:40 Rogier Wolff wrote:
> > 
> > While working on SPI and I2C support for the BCM2835, I found the
> > BCM63xx SPI driver in the kernel. Turns out that this support
> > was partially merged: 
> > 
> > The support can only be enabled when BCM63xx configuration symbol
> > is defined which menuconfig lists as: 
> > 
> >  Symbol: BCM63XX [=BCM63XX]                                                
> >    Type  : unknown                                                           
> > 
> > I'd say the definition of this is not possible through the normal
> > channels.
> > 
> > And in the driver (drivers/spi/spi-bcm63xx.c) I see: 
> > 
> > #include <bcm63xx_dev_spi.h>
> > 
> > but that file is not in the current git release.
> 
> No, it did not make it for a reason I ignore, probably miscommunication.
> 
> > 
> > (some more googling has resulted in me finding out that I don't want
> > to know how the 63xx SPI controller works as it's for a MIPS processor
> > while the 2835 is ARM).

> And so? if the core is the same, just use it on your platform
> too. If you have a look at the architecture files, you will see that
> the various BCM63xx SoC have their internal registers shuffled but
> the SPI core is always software compatible, another set of registers
> can be added for BCM2835.

I expect the core to be very different because they are for different
processors. But of course if they are the same, a single driver would
be better. 

However, with the header file missing, I can't find if the register
offsets are the same. That would be a hint that the module is the the
same. 

Reading the driver I see lots "readb" and "writeb" calls. These
presumably read/write a byte. The '2835 module doesn't have any
byte-registers. All registers are 32bits. I consider this a further
hint that the modules are not the same. 

I've read some of the code, and for instance, there seems to be a
limited-width register (3 or 4 bits) that specify the clock rate on
the bcm63xx. On the bcm2835 the clock is set by good chunk (15 bits
IIRC) of a 32-bit register which specifies the clock divisor. The core
clock runs at 250MHz, so I can specify clock rates at with 1:250
accuracy around 1MHz. (i.e. 1000000 Hz is possible as well as 1004000)
I consider this a further hint that the modules are not the same. 

So with three of those hints I'll take the hint that they are not the
same, and concentrate on building a new driver for the bcm2835 (and
2708?)

	Roger. 


-- 
** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2600998 **
**    Delftechpark 26 2628 XH  Delft, The Netherlands. KVK: 27239233    **
*-- BitWizard writes Linux device drivers for any device you may have! --*
The plan was simple, like my brother-in-law Phil. But unlike
Phil, this plan just might work.