[PATCH] drm: aux ->transfer() can return 0, deal with it

[PATCH] drm: aux ->transfer() can return 0, deal with it

[ville.syrjala]

From: Ville Syrjälä <ville.syrjala@linux.intel.com>

Restore the correct behaviour (as in check msg.reply) when aux
->transfer() returns 0. It got removed in
commit 82922da39190 ("drm/dp_helper: Retry aux transactions on all errors")

Now I can actually dump the "entire" DPCD on a Dell UP2314Q with
ddrescue. It has some offsets in the DPCD that can't be read
for some resaon, all you get is defers. Previously ddrescue would
just give up at the first unredable offset on account of
read() returning 0 means EOF. Here's the ddrescue log
for the interested:
0x00000000  0x00001400  +
0x00001400  0x00000030  -
0x00001430  0x000001D0  +
0x00001600  0x00000030  -
0x00001630  0x0001F9D0  +
0x00021000  0x00000001  -
0x00021001  0x000DEFFF  +

Cc: Lyude <cpaul@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch
Cc: stable@vger.kernel.org
Fixes: 82922da39190 ("drm/dp_helper: Retry aux transactions on all errors")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 091053e995e5..8f11b8741e42 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -203,7 +203,7 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 
 		ret = aux->transfer(aux, &msg);
 
-		if (ret > 0) {
+		if (ret >= 0) {
 			native_reply = msg.reply & DP_AUX_NATIVE_REPLY_MASK;
 			if (native_reply == DP_AUX_NATIVE_REPLY_ACK) {
 				if (ret == size)
-- 
2.7.4

Re: [PATCH] drm: aux ->transfer() can return 0, deal with it

[Daniel Vetter]

On Thu, Jul 28, 2016 at 05:54:42PM +0300, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrj�l� <ville.syrjala@linux.intel.com>
> 
> Restore the correct behaviour (as in check msg.reply) when aux
> ->transfer() returns 0. It got removed in
> commit 82922da39190 ("drm/dp_helper: Retry aux transactions on all errors")
> 
> Now I can actually dump the "entire" DPCD on a Dell UP2314Q with
> ddrescue. It has some offsets in the DPCD that can't be read
> for some resaon, all you get is defers. Previously ddrescue would
> just give up at the first unredable offset on account of
> read() returning 0 means EOF. Here's the ddrescue log
> for the interested:
> 0x00000000  0x00001400  +
> 0x00001400  0x00000030  -
> 0x00001430  0x000001D0  +
> 0x00001600  0x00000030  -
> 0x00001630  0x0001F9D0  +
> 0x00021000  0x00000001  -
> 0x00021001  0x000DEFFF  +
> 
> Cc: Lyude <cpaul@redhat.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch
> Cc: stable@vger.kernel.org
> Fixes: 82922da39190 ("drm/dp_helper: Retry aux transactions on all errors")
> Signed-off-by: Ville Syrj�l� <ville.syrjala@linux.intel.com>

Seems to correctly restore that special case.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Dave, since I just send out a drm-misc pull, can you pls apply this one
directly to drm-next?
-Daniel

> ---
>  drivers/gpu/drm/drm_dp_helper.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 091053e995e5..8f11b8741e42 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -203,7 +203,7 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
>  
>  		ret = aux->transfer(aux, &msg);
>  
> -		if (ret > 0) {
> +		if (ret >= 0) {
>  			native_reply = msg.reply & DP_AUX_NATIVE_REPLY_MASK;
>  			if (native_reply == DP_AUX_NATIVE_REPLY_ACK) {
>  				if (ret == size)
> -- 
> 2.7.4
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch