[RFC 2/2] gpu: ipu-v3: reset DMFC memory when disabling

[Ying Liu]

On Mon, Aug 29, 2016 at 6:33 PM, Philipp Zabel <p.zabel at pengutronix.de> wrote:
> Reset the write FIFO memories after disabling the DMFC
> to make sure no stale data is kept around.
>
> Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
> ---
>  drivers/gpu/ipu-v3/ipu-dmfc.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/ipu-v3/ipu-dmfc.c b/drivers/gpu/ipu-v3/ipu-dmfc.c
> index a40f211..e1e5506 100644
> --- a/drivers/gpu/ipu-v3/ipu-dmfc.c
> +++ b/drivers/gpu/ipu-v3/ipu-dmfc.c
> @@ -131,8 +131,10 @@ void ipu_dmfc_disable_channel(struct dmfc_channel *dmfc)
>
>         priv->use_count--;
>
> -       if (!priv->use_count)
> +       if (!priv->use_count) {
>                 ipu_module_disable(priv->ipu, IPU_CONF_DMFC_EN);
> +               ipu_memory_reset(priv->ipu, IPU_RST_MEM_DMFC_WR);

We've got use counter for DMFC as DMFC can be used by several channels
simultaneously.  That means only the last user may trigger the DMFC_WR
memory reset operation.  I assume this is not what we want - we need
every channel's dedicated DMFC write memory could be reset separately.
However, it looks that the hardware hasn't got the capability to do that.
I think writing 1 to DMFC_WR resets all DMFC writing channels' memory.

Regards,
Liu Ying

> +       }
>
>         if (priv->use_count < 0)
>                 priv->use_count = 0;
> --
> 2.8.1
>