[U-Boot] [PATCH v3 1/3] cmd_sf: add 'release' command

[Simon Glass]

Hi,

On 20 November 2015 at 03:13, Valentin Longchamp
<valentin.longchamp at keymile.com> wrote:
> On 19/11/2015 17:57, Jagan Teki wrote:
>> On 13 November 2015 at 18:55, Valentin Longchamp
>> <valentin.longchamp at keymile.com> wrote:
>>> The release command is the pendant of the probe command. This command
>>> allows to call spi_flash_free from the command line. This may be
>>> necessary for some boards where sf probe does change the state of the
>>> hardware (like with some pin multiplexing changes for instance).
>>
>> So you want to change the state of pin multiplexing on your board with
>> connected slave devices example: spi nor flash is it? what exactly the
>> need of releasing? why can't we use pin multiplexing changes like
>> selecting or deselecting particular lines through driver or from board
>> files itself.
>
> That's our use case yes. Let me explain you it again in detail. Some of the
> signals used to access the NAND Flash and the SPI NOR are shared. At reset, they
> are available for the SPI NOR, since u-boot is in there and the CPU then
> accesses it.
>
> In an usual boot sequence, the SPI NOR is accessed first (copying u-boot to the
> RAM, reading out the environment) and so the pins are configured in hardware at
> boot time for accessing the SPI NOR. After that, they are configured to access
> the NAND where the kernel and filesystem are stored to boot Linux thanks to
> env_relocate_spec() calling spi_flash_free() on exit in conjunction with [1]
>
> Now in the case where the boot sequence is interrupted and some accesses are
> done to the SPI NOR, the pins are changed again to SPI NOR to perform these
> accesses. But we have to make sure that the pins are configured back to NAND by
> calling spi_flash_free() after these accesses and that's why I introduced the
> release() function.
>
> In our case, there are 2 types of such accesses:
> - environment variables write: this is the first patch of the series. It simply
> adds calls to spi_flash_free() at function exit no only in env_relocate_spec()
> but also in saveenv() so that the behavior here is coherent for the whole env_sf
> file (spi_flash_probe() at function start, spi_flash_free() at function exit).
> - updating u-boot: this is solved for us with the last 2 patches of the series.
> The first one just adds a sf release command that does the opposite/cleanup to
> sf probe and the second patch just calls this command in our scripts where
> u-boot is updated/the SPI NOR is written.
>
> We are *indeed* using pin multiplexing changes, in our case, they are
> implemented in the spi controller driver: drivers/spi/kirkwood_spi.c. To be very
> specific, in our case this sf release command allows to explicitely call
> spi_flash_free() which calls spi_free_slave(), which in our case
> (kirkwood_spi.c) sets the pins back to their previous configuration.

Does your board use driver model from SPI and SPI flash? If not I
think that should be the first step.

Regards,
Simon
[snip]