[U-Boot] [u-boot][RFC v1] omap_hsmmc: omap4+/am335x: modify MMC controller internal fsm reset func

[Pantelis Antoniou]

Hi Oleksandr

On Aug 6, 2013, at 1:44 PM, Oleksandr Tyshchenko wrote:

> "mmc_send_cmd: timeout: No status update" error sometimes happens in
> omap_hsmmc driver func mmc_send_cmd() when the MMC controller card
> identification and selection sequence is executed for eMMC on OMAP4
> boards.
> 
> It happens due to incorrect execution of CMD line reset procedure
> for OMAP4. Because CMD(DAT) lines reset procedures are slightly
> different for OMAP3 and OMAP4(AM335x,OMAP5,DRA7xx).
> 
> According to OMAP3 TRM:
> Set SRC(SRD) bit in MMCHS_SYSCTL register to 0x1 and wait until
> it returns to 0x0.
> 
> According to OMAP4(AM335x,OMAP5,DRA7xx) TRMs, CMD(DATA) lines reset
> procedure steps must be as follows:
> 1. Initiate CMD(DAT) line reset by writing 0x1 to SRC(SRD) bit in
>   MMCHS_SYSCTL register (SD_SYSCTL for AM335x).
> 2. Poll the SRC(SRD) bit until it is set to 0x1.
> 3. Wait until the SRC(SRD) bit returns to 0x0
>  (reset procedure is completed).
> 
> Unfortunately, at present omap_hsmmc driver has support only for
> OMAP3. And as result step #2 is missing for OMAP4(AM335x,OMAP5,DRA7xx).
> This sometimes leads to the fact that the waiting loop which is
> required in step #3 does not executed, because SRC bit does not set
> yet (at the moment of checking a condition of a loop execution).
> And as a result this can cause to timeout error when sending a
> next command.
> 
> In the particular case (working with eMMC witch do not respond to
> some SD specific command) due to incorrect reset sequence after
> command SD_CMD_SEND_IF_COND which finished with CTO flag within
> 64 clock cycles, the next command MMC_CMD_APP_CMD leads to a
> timeout error within 1s.
> 
> So, extend CMD(DATA) lines reset procedure in func
> mmc_reset_controller_fsm() by adding the missing step #2 for
> OMAP4+/AM335x boards.
> 
> Signed-off-by: Oleksandr Tyshchenko <oleksandr.tyshchenko at ti.com>

Acked-by: Pantelis Antoniou <panto at antoniou-consulting.com>

Thanks