[U-Boot] Environment and SPI drivers

[Albin Tonnerre <albin.tonnerre@free-electrons.com>]

On Mon, 15 Mar 2010 21:25 +0100, Wolfgang Denk wrote :
> Dear Albin Tonnerre,
> 
> In message <20100315192914.GA14032@pc-ran3241> you wrote:
> > 
> > The SPI framework provided by u-boot (spi_setup_slave, spi_xfer and the like)
> > cannot currently be used to read the environment from SPI devices. The reason is
> 
> This depends on what sort of SPI devices you are talking about. Do you
> have plain simple EEPROM in mind, or things like SPI flash, or
> eventually MMC/SDCard?  These are pretty different thinngs...

In this particular case, mostly EEPROM, but that would apply to anything trying
to use the SPI framework before mem_malloc_init is called.

> 
> > I'm wondering what would be a proper fix for this. I don't think it is OK to say
> > 'drivers reading the environment should not use the SPI framework', as those
> > drivers might be used to do others things - that would make the SPI framework
> > unsuitable for (e.g.) any SPI EEPROM. The only sane alternative I can see is
> > that we introduce spi_setup_slave_$whatever, which would work the same way as
> > spi_setup_slave, with the difference that it should be given caller-allocated
> > storage, so that we avoid the use for malloc().
> 
> If you are talking about SPI EEPROM, then just enable EEPROM support
> and environment in EEPROM, and set CONFIG_SPI. The EEPROM framework in
> "common/cmd_eeprom.c" includes support for SPI EEPROM (this actually
> predates the SPI framework).

I know, I did that. The thing is, even with the support for SPI EEPROM, you
need a driver to actually issue the proper commands to read/write data from/to
the SPI EEPROM -- that is, implement spi_read/write. If you do that using the
SPI framework as, I guess, one would expect, then you're screwed since all the
implementations of spi_setup_slave call malloc(), and you can't read your
environment.

Regards,
-- 
Albin Tonnerre, Free Electrons
Kernel, drivers and embedded Linux development,
consulting, training and support.
http://free-electrons.com