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SubjectRe: [PATCHv2] ASoC: fsl: imx-ssi: omit ssi counter to avoid harm in unbalanced situation
Someone around who would like to add his acked-by?

thanks,
Oskar

On Sat, Nov 16, 2013 at 07:52:25 +0000, Oskar Schirmer wrote:
> Unbalanced calls to imx_ssi_trigger() may result in endless
> SSI activity and thus provoke eternal sound. While on the first glance,
> the switch statement looks pretty symmetric, the SUSPEND/RESUME
> pair is not: the suspend case comes along snd_pcm_suspend_all(),
> which for fsl/imx-pcm-fiq is called only at snd_soc_suspend(),
> but the resume case originates straight from the SNDRV_PCM_IOCTL_RESUME.
> This way userland may provoke an unbalanced resume, which might cause
> the ssi->enabled counter to increase and never return to zero again,
> so eventually SSI_SCR_SSIEN is never disabled.
>
> As the information on whether to enable the SSI or not is contained
> in the two bits for TE/RE, we save all the software mirroring of
> hardware state here and simply use the hardware register itself
> to keep the state of whether someone is currently playing or capturing.
>
> This is essentially the same stuff as in sound/soc/fsl/imx-pcm-fiq.c
> which I send a patch for three days ago. Astonishing enough this
> highly fragile scheme is used twice in parallel to serve the very
> same control function, synchronously: Once out of sync you are lost
> until reboot.
>
> Note, that these fixes wont prevent state machine distortion on alsa
> level to cut sound or the like. It just makes sure we have a chance
> to synchronise again later on.
>
> Signed-off-by: Oskar Schirmer <oskar@scara.com>
> ---
> v2: drop all software flag handling in favour of hardware registers
>
> sound/soc/fsl/imx-ssi.c | 5 ++---
> sound/soc/fsl/imx-ssi.h | 1 -
> 2 files changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/sound/soc/fsl/imx-ssi.c b/sound/soc/fsl/imx-ssi.c
> index f5f248c..2eb2691 100644
> --- a/sound/soc/fsl/imx-ssi.c
> +++ b/sound/soc/fsl/imx-ssi.c
> @@ -304,8 +304,7 @@ static int imx_ssi_trigger(struct snd_pcm_substream *substream, int cmd,
> scr |= SSI_SCR_RE;
> sier |= sier_bits;
>
> - if (++ssi->enabled == 1)
> - scr |= SSI_SCR_SSIEN;
> + scr |= SSI_SCR_SSIEN;
>
> break;
>
> @@ -318,7 +317,7 @@ static int imx_ssi_trigger(struct snd_pcm_substream *substream, int cmd,
> scr &= ~SSI_SCR_RE;
> sier &= ~sier_bits;
>
> - if (--ssi->enabled == 0)
> + if (!(scr & (SSI_SCR_TE | SSI_SCR_RE)))
> scr &= ~SSI_SCR_SSIEN;
>
> break;
> diff --git a/sound/soc/fsl/imx-ssi.h b/sound/soc/fsl/imx-ssi.h
> index 560c40f..be65623 100644
> --- a/sound/soc/fsl/imx-ssi.h
> +++ b/sound/soc/fsl/imx-ssi.h
> @@ -213,7 +213,6 @@ struct imx_ssi {
>
> int fiq_init;
> int dma_init;
> - int enabled;
> };
>
> #endif /* _IMX_SSI_H */
> --
> 1.7.9.5
>
>


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