Re: [PATCH] drm/amd/display: use a more accurate check in dm_helpers_dp_read_dpcd()
On 3/10/23 12:51, Ville Syrjälä wrote: > On Fri, Mar 10, 2023 at 07:48:04PM +0200, Ville Syrjälä wrote: >> On Thu, Mar 09, 2023 at 04:30:27PM -0500, Hamza Mahfooz wrote: >>> We should be checking if drm_dp_dpcd_read() returns the size that we are >>> asking it to read instead of just checking if it is greater than zero. >>> Also, we should WARN_ON() here since this condition is only ever met, if >>> there is an issue worth investigating. So, compare the return value of >>> drm_dp_dpcd_read() to size and WARN_ON() if they aren't equal. >>> >>> Signed-off-by: Hamza Mahfooz >>> --- >>> drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c >>> b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c >>> index 8d598b322e5b..ed2ed7b1d869 100644 >>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c >>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c >>> @@ -511,8 +511,8 @@ bool dm_helpers_dp_read_dpcd( >>> return false; >>> } >>> >>> - return drm_dp_dpcd_read(>dm_dp_aux.aux, address, >>> - data, size) > 0; >>> + return !WARN_ON(drm_dp_dpcd_read(>dm_dp_aux.aux, address, >>> +data, size) != size); >> >> Just FYI there are devices out there that violate the DP spec and reads >> from specific DPCD registers simply fail instead of returning the >> expected 0. > > And of course anyone can yank the cable anytime, so in > fact pretty much any DPCD read can fail. > Thanks for making this very important point. It seems like drm_dp_dpcd_access checks for that, though, and returns -EPROTO if !(ret == size). So I don't expect this patch to change any behavior. Harry
Re: [PATCH] drm/amd/display: use a more accurate check in dm_helpers_dp_read_dpcd()
On Fri, Mar 10, 2023 at 07:48:04PM +0200, Ville Syrjälä wrote: > On Thu, Mar 09, 2023 at 04:30:27PM -0500, Hamza Mahfooz wrote: > > We should be checking if drm_dp_dpcd_read() returns the size that we are > > asking it to read instead of just checking if it is greater than zero. > > Also, we should WARN_ON() here since this condition is only ever met, if > > there is an issue worth investigating. So, compare the return value of > > drm_dp_dpcd_read() to size and WARN_ON() if they aren't equal. > > > > Signed-off-by: Hamza Mahfooz > > --- > > drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c > > b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c > > index 8d598b322e5b..ed2ed7b1d869 100644 > > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c > > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c > > @@ -511,8 +511,8 @@ bool dm_helpers_dp_read_dpcd( > > return false; > > } > > > > - return drm_dp_dpcd_read(>dm_dp_aux.aux, address, > > - data, size) > 0; > > + return !WARN_ON(drm_dp_dpcd_read(>dm_dp_aux.aux, address, > > +data, size) != size); > > Just FYI there are devices out there that violate the DP spec and reads > from specific DPCD registers simply fail instead of returning the > expected 0. And of course anyone can yank the cable anytime, so in fact pretty much any DPCD read can fail. -- Ville Syrjälä Intel
Re: [PATCH] drm/amd/display: use a more accurate check in dm_helpers_dp_read_dpcd()
On Thu, Mar 09, 2023 at 04:30:27PM -0500, Hamza Mahfooz wrote: > We should be checking if drm_dp_dpcd_read() returns the size that we are > asking it to read instead of just checking if it is greater than zero. > Also, we should WARN_ON() here since this condition is only ever met, if > there is an issue worth investigating. So, compare the return value of > drm_dp_dpcd_read() to size and WARN_ON() if they aren't equal. > > Signed-off-by: Hamza Mahfooz > --- > drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c > b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c > index 8d598b322e5b..ed2ed7b1d869 100644 > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c > @@ -511,8 +511,8 @@ bool dm_helpers_dp_read_dpcd( > return false; > } > > - return drm_dp_dpcd_read(>dm_dp_aux.aux, address, > - data, size) > 0; > + return !WARN_ON(drm_dp_dpcd_read(>dm_dp_aux.aux, address, > + data, size) != size); Just FYI there are devices out there that violate the DP spec and reads from specific DPCD registers simply fail instead of returning the expected 0. > } > > bool dm_helpers_dp_write_dpcd( > -- > 2.39.2 -- Ville Syrjälä Intel
Re: [PATCH] drm/amd/display: use a more accurate check in dm_helpers_dp_read_dpcd()
On 3/9/23 14:30, Hamza Mahfooz wrote: We should be checking if drm_dp_dpcd_read() returns the size that we are asking it to read instead of just checking if it is greater than zero. Also, we should WARN_ON() here since this condition is only ever met, if there is an issue worth investigating. So, compare the return value of drm_dp_dpcd_read() to size and WARN_ON() if they aren't equal. Signed-off-by: Hamza Mahfooz --- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c index 8d598b322e5b..ed2ed7b1d869 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c @@ -511,8 +511,8 @@ bool dm_helpers_dp_read_dpcd( return false; } - return drm_dp_dpcd_read(>dm_dp_aux.aux, address, - data, size) > 0; + return !WARN_ON(drm_dp_dpcd_read(>dm_dp_aux.aux, address, +data, size) != size); } bool dm_helpers_dp_write_dpcd( Reviewed-by: Rodrigo Siqueira and pushed to amd-staging-drm-next. Thanks Siqueira
[PATCH] drm/amd/display: use a more accurate check in dm_helpers_dp_read_dpcd()
We should be checking if drm_dp_dpcd_read() returns the size that we are asking it to read instead of just checking if it is greater than zero. Also, we should WARN_ON() here since this condition is only ever met, if there is an issue worth investigating. So, compare the return value of drm_dp_dpcd_read() to size and WARN_ON() if they aren't equal. Signed-off-by: Hamza Mahfooz --- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c index 8d598b322e5b..ed2ed7b1d869 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c @@ -511,8 +511,8 @@ bool dm_helpers_dp_read_dpcd( return false; } - return drm_dp_dpcd_read(>dm_dp_aux.aux, address, - data, size) > 0; + return !WARN_ON(drm_dp_dpcd_read(>dm_dp_aux.aux, address, +data, size) != size); } bool dm_helpers_dp_write_dpcd( -- 2.39.2
