[PATCH] drm/dp: retry AUX transactions 32 times (v1.1)

[Alex Deucher]

On Tue, Nov 25, 2014 at 10:25 PM, Dave Airlie <airlied at gmail.com> wrote:
> From: Dave Airlie <airlied at redhat.com>
>
> At least on two MST devices I've tested with, when
> they are link training downstream, they are totally
> unable to handle aux ch msgs, so they defer like nuts.
> I tried 16, it wasn't enough, 32 seems better.
>
> This fixes one Dell 4k monitor and one of the
> MST hubs.
>
> v1.1: fixup comment (Tom).
>
> Signed-off-by: Dave Airlie <airlied at redhat.com>

Acked-by: Alex Deucher <alexander.deucher at amd.com>

> ---
>  drivers/gpu/drm/drm_dp_helper.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 959e207..79968e3 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -186,10 +186,11 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
>
>         /*
>          * The specification doesn't give any recommendation on how often to
> -        * retry native transactions, so retry 7 times like for I2C-over-AUX
> -        * transactions.
> +        * retry native transactions. We used to retry 7 times like for
> +        * aux i2c transactions but real world devices this wasn't
> +        * sufficient, bump to 32 which makes Dell 4k monitors happier.
>          */
> -       for (retry = 0; retry < 7; retry++) {
> +       for (retry = 0; retry < 32; retry++) {
>
>                 mutex_lock(&aux->hw_mutex);
>                 err = aux->transfer(aux, &msg);
> --
> 2.1.0
>
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