Re: [alsa-devel] [PATCH v2 1/1] ASoC: fsl_ssi: add CCSR_SSI_SOR to volatile register list

[Fabio Estevam]

On Mon, Apr 25, 2016 at 3:36 PM, Caleb Crome <caleb@xxxxxxxxx> wrote:
> The CCSR_SSI_SOR is a register that clears the TX and/or the RX fifo
> on the i.MX SSI port.  The fsl_ssi_trigger writes this register in
> order to clear the fifo at trigger time.
>
> However, since the CCSR_SSI_SOR register is not in the volatile list,
> the caching mechanism prevented the register write in the trigger
> function.  This caused the fifo to not be cleared (because the value
> was unchanged from the last time the register was written), and thus
> causes the channels in both TDM or simple I2S mode to slip and be in
> the wrong time slots on SSI restart.
>
> This has gone unnoticed for so long because with simple stereo mode,
> the consequence is that left and right are swapped, which isn't that
> noticeable.  However, it's catestrophic in some systems that
> require the channels to be in the right slots.
>
> Signed-off-by: Caleb Crome <caleb@xxxxxxxxx>
> Suggested-by: Arnaud Mouiche <arnaud.mouiche@xxxxxxxxxxx>

Reviewed-by: Fabio Estevam <fabio.estevam@xxxxxxx>