[PATCH] drm: mxsfb: Set proper default bus format when using a bridge

[PATCH] drm: mxsfb: Set proper default bus format when using a bridge

[Guido Günther]

If a bridge doesn't do any bus format handling MEDIA_BUS_FMT_FIXED is
returned. Fallback to a reasonable default (MEDIA_BUS_FMT_RGB888_1X24) in
that case.

This unbreaks e.g. using mxsfb with the nwl bridge and mipi panels.

Fixes: b776b0f00f24 ("drm: mxsfb: Use bus_format from the nearest bridge if present")

Signed-off-by: Guido Günther <agx@sigxcpu.org>
---

I'll look at what needs to be done in nwl separately but this also
unbreaks other bridge seupts that don't to format negotiation yet.

 drivers/gpu/drm/mxsfb/mxsfb_kms.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
index af6c620adf6e..4ef94cf686b0 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
+++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
@@ -369,6 +369,8 @@ static void mxsfb_crtc_atomic_enable(struct drm_crtc *crtc,
 			drm_atomic_get_new_bridge_state(state,
 							mxsfb->bridge);
 		bus_format = bridge_state->input_bus_cfg.format;
+		if (bus_format == MEDIA_BUS_FMT_FIXED)
+			bus_format = MEDIA_BUS_FMT_RGB888_1X24;
 	}
 
 	/* If there is no bridge, use bus format from connector */
-- 
2.33.0

Re: [PATCH] drm: mxsfb: Set proper default bus format when using a bridge

[Marek Vasut]

On 9/28/21 10:55 AM, Guido Günther wrote:
> If a bridge doesn't do any bus format handling MEDIA_BUS_FMT_FIXED is
> returned. Fallback to a reasonable default (MEDIA_BUS_FMT_RGB888_1X24) in
> that case.
> 
> This unbreaks e.g. using mxsfb with the nwl bridge and mipi panels.
> 
> Fixes: b776b0f00f24 ("drm: mxsfb: Use bus_format from the nearest bridge if present")
> 
> Signed-off-by: Guido Günther <agx@sigxcpu.org>
> ---
> 
> I'll look at what needs to be done in nwl separately but this also
> unbreaks other bridge seupts that don't to format negotiation yet.
> 
>   drivers/gpu/drm/mxsfb/mxsfb_kms.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> index af6c620adf6e..4ef94cf686b0 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> @@ -369,6 +369,8 @@ static void mxsfb_crtc_atomic_enable(struct drm_crtc *crtc,
>   			drm_atomic_get_new_bridge_state(state,
>   							mxsfb->bridge);
>   		bus_format = bridge_state->input_bus_cfg.format;
> +		if (bus_format == MEDIA_BUS_FMT_FIXED)
> +			bus_format = MEDIA_BUS_FMT_RGB888_1X24;

Shouldn't the NWL bridge return the correct format ?

Re: [PATCH] drm: mxsfb: Set proper default bus format when using a bridge

[Guido Günther]

Hi,
On Tue, Sep 28, 2021 at 11:08:58AM +0200, Marek Vasut wrote:
> On 9/28/21 10:55 AM, Guido Günther wrote:
> > If a bridge doesn't do any bus format handling MEDIA_BUS_FMT_FIXED is
> > returned. Fallback to a reasonable default (MEDIA_BUS_FMT_RGB888_1X24) in
> > that case.
> > 
> > This unbreaks e.g. using mxsfb with the nwl bridge and mipi panels.
> > 
> > Fixes: b776b0f00f24 ("drm: mxsfb: Use bus_format from the nearest bridge if present")
> > 
> > Signed-off-by: Guido Günther <agx@sigxcpu.org>
> > ---
> > 
> > I'll look at what needs to be done in nwl separately but this also
> > unbreaks other bridge seupts that don't to format negotiation yet.
> > 
> >   drivers/gpu/drm/mxsfb/mxsfb_kms.c | 2 ++
> >   1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > index af6c620adf6e..4ef94cf686b0 100644
> > --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > @@ -369,6 +369,8 @@ static void mxsfb_crtc_atomic_enable(struct drm_crtc *crtc,
> >   			drm_atomic_get_new_bridge_state(state,
> >   							mxsfb->bridge);
> >   		bus_format = bridge_state->input_bus_cfg.format;
> > +		if (bus_format == MEDIA_BUS_FMT_FIXED)
> > +			bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> 
> Shouldn't the NWL bridge return the correct format ?

Yes it should and I'll send a separate patch for that but we currently
don't do anything meaningful at all if the bridge doesn't do format
negotiation and then fail setup in mxsfb_set_formats().

I think we should at least preserve the status quo (as we do with the
non bridge case in b776b0f00f24 too).

We could have a warning to spot drivers that don't do that yet and hence
the generic code returns MEDIA_BUS_FMT_FIXED.

Cheers,
 -- Guido

Re: [PATCH] drm: mxsfb: Set proper default bus format when using a bridge

[Marek Vasut]

On 9/28/21 11:19 AM, Guido Günther wrote:
> Hi,
> On Tue, Sep 28, 2021 at 11:08:58AM +0200, Marek Vasut wrote:
>> On 9/28/21 10:55 AM, Guido Günther wrote:
>>> If a bridge doesn't do any bus format handling MEDIA_BUS_FMT_FIXED is
>>> returned. Fallback to a reasonable default (MEDIA_BUS_FMT_RGB888_1X24) in
>>> that case.
>>>
>>> This unbreaks e.g. using mxsfb with the nwl bridge and mipi panels.
>>>
>>> Fixes: b776b0f00f24 ("drm: mxsfb: Use bus_format from the nearest bridge if present")
>>>
>>> Signed-off-by: Guido Günther <agx@sigxcpu.org>
>>> ---
>>>
>>> I'll look at what needs to be done in nwl separately but this also
>>> unbreaks other bridge seupts that don't to format negotiation yet.
>>>
>>>    drivers/gpu/drm/mxsfb/mxsfb_kms.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
>>> index af6c620adf6e..4ef94cf686b0 100644
>>> --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
>>> +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
>>> @@ -369,6 +369,8 @@ static void mxsfb_crtc_atomic_enable(struct drm_crtc *crtc,
>>>    			drm_atomic_get_new_bridge_state(state,
>>>    							mxsfb->bridge);
>>>    		bus_format = bridge_state->input_bus_cfg.format;
>>> +		if (bus_format == MEDIA_BUS_FMT_FIXED)
>>> +			bus_format = MEDIA_BUS_FMT_RGB888_1X24;
>>
>> Shouldn't the NWL bridge return the correct format ?
> 
> Yes it should and I'll send a separate patch for that but we currently
> don't do anything meaningful at all if the bridge doesn't do format
> negotiation and then fail setup in mxsfb_set_formats().
> 
> I think we should at least preserve the status quo (as we do with the
> non bridge case in b776b0f00f24 too).
> 
> We could have a warning to spot drivers that don't do that yet and hence
> the generic code returns MEDIA_BUS_FMT_FIXED.

I am not gonna push back against this patch, I think you need feedback 
from the drm people on this. A warning would indeed be nice. Preserving 
the old behavior in stable releases would be good (if there are any 
releases which contain the mxsfb patch this fixes).

Re: [PATCH] drm: mxsfb: Set proper default bus format when using a bridge

[Lucas Stach]

Am Dienstag, dem 28.09.2021 um 11:19 +0200 schrieb Guido Günther:
> Hi,
> On Tue, Sep 28, 2021 at 11:08:58AM +0200, Marek Vasut wrote:
> > On 9/28/21 10:55 AM, Guido Günther wrote:
> > > If a bridge doesn't do any bus format handling MEDIA_BUS_FMT_FIXED is
> > > returned. Fallback to a reasonable default (MEDIA_BUS_FMT_RGB888_1X24) in
> > > that case.
> > > 
> > > This unbreaks e.g. using mxsfb with the nwl bridge and mipi panels.
> > > 
> > > Fixes: b776b0f00f24 ("drm: mxsfb: Use bus_format from the nearest bridge if present")
> > > 
> > > Signed-off-by: Guido Günther <agx@sigxcpu.org>
> > > ---
> > > 
> > > I'll look at what needs to be done in nwl separately but this also
> > > unbreaks other bridge seupts that don't to format negotiation yet.
> > > 
> > >   drivers/gpu/drm/mxsfb/mxsfb_kms.c | 2 ++
> > >   1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > > index af6c620adf6e..4ef94cf686b0 100644
> > > --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > > +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > > @@ -369,6 +369,8 @@ static void mxsfb_crtc_atomic_enable(struct drm_crtc *crtc,
> > >   			drm_atomic_get_new_bridge_state(state,
> > >   							mxsfb->bridge);
> > >   		bus_format = bridge_state->input_bus_cfg.format;
> > > +		if (bus_format == MEDIA_BUS_FMT_FIXED)
> > > +			bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> > 
> > Shouldn't the NWL bridge return the correct format ?
> 
> Yes it should and I'll send a separate patch for that but we currently
> don't do anything meaningful at all if the bridge doesn't do format
> negotiation and then fail setup in mxsfb_set_formats().
> 
> I think we should at least preserve the status quo (as we do with the
> non bridge case in b776b0f00f24 too).
> 
> We could have a warning to spot drivers that don't do that yet and hence
> the generic code returns MEDIA_BUS_FMT_FIXED.
> 
That sounds sensible. Using a default format if we don't know what to
do is going to be a unpleasant surprise for those with a display
pipeline that doesn't work with the default format. So please add a
dev_warn when we are doing this fallback.

Also I would argue that the NWL fix is the patch that should go in the
stable tree. This one should only be a additional safety net, so I
would drop the Fixes tag.

Regards,
Lucas

Re: [PATCH] drm: mxsfb: Set proper default bus format when using a bridge

[Marek Vasut]

On 9/28/21 11:27 AM, Lucas Stach wrote:
> Am Dienstag, dem 28.09.2021 um 11:19 +0200 schrieb Guido Günther:
>> Hi,
>> On Tue, Sep 28, 2021 at 11:08:58AM +0200, Marek Vasut wrote:
>>> On 9/28/21 10:55 AM, Guido Günther wrote:
>>>> If a bridge doesn't do any bus format handling MEDIA_BUS_FMT_FIXED is
>>>> returned. Fallback to a reasonable default (MEDIA_BUS_FMT_RGB888_1X24) in
>>>> that case.
>>>>
>>>> This unbreaks e.g. using mxsfb with the nwl bridge and mipi panels.
>>>>
>>>> Fixes: b776b0f00f24 ("drm: mxsfb: Use bus_format from the nearest bridge if present")
>>>>
>>>> Signed-off-by: Guido Günther <agx@sigxcpu.org>
>>>> ---
>>>>
>>>> I'll look at what needs to be done in nwl separately but this also
>>>> unbreaks other bridge seupts that don't to format negotiation yet.
>>>>
>>>>    drivers/gpu/drm/mxsfb/mxsfb_kms.c | 2 ++
>>>>    1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
>>>> index af6c620adf6e..4ef94cf686b0 100644
>>>> --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
>>>> +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
>>>> @@ -369,6 +369,8 @@ static void mxsfb_crtc_atomic_enable(struct drm_crtc *crtc,
>>>>    			drm_atomic_get_new_bridge_state(state,
>>>>    							mxsfb->bridge);
>>>>    		bus_format = bridge_state->input_bus_cfg.format;
>>>> +		if (bus_format == MEDIA_BUS_FMT_FIXED)
>>>> +			bus_format = MEDIA_BUS_FMT_RGB888_1X24;
>>>
>>> Shouldn't the NWL bridge return the correct format ?
>>
>> Yes it should and I'll send a separate patch for that but we currently
>> don't do anything meaningful at all if the bridge doesn't do format
>> negotiation and then fail setup in mxsfb_set_formats().
>>
>> I think we should at least preserve the status quo (as we do with the
>> non bridge case in b776b0f00f24 too).
>>
>> We could have a warning to spot drivers that don't do that yet and hence
>> the generic code returns MEDIA_BUS_FMT_FIXED.
>>
> That sounds sensible. Using a default format if we don't know what to
> do is going to be a unpleasant surprise for those with a display
> pipeline that doesn't work with the default format. So please add a
> dev_warn when we are doing this fallback.
> 
> Also I would argue that the NWL fix is the patch that should go in the
> stable tree. This one should only be a additional safety net, so I
> would drop the Fixes tag.

Indeed

Re: [PATCH] drm: mxsfb: Set proper default bus format when using a bridge

[Guido Günther]

Hi,
On Tue, Sep 28, 2021 at 11:27:49AM +0200, Lucas Stach wrote:
> Am Dienstag, dem 28.09.2021 um 11:19 +0200 schrieb Guido Günther:
> > Hi,
> > On Tue, Sep 28, 2021 at 11:08:58AM +0200, Marek Vasut wrote:
> > > On 9/28/21 10:55 AM, Guido Günther wrote:
> > > > If a bridge doesn't do any bus format handling MEDIA_BUS_FMT_FIXED is
> > > > returned. Fallback to a reasonable default (MEDIA_BUS_FMT_RGB888_1X24) in
> > > > that case.
> > > > 
> > > > This unbreaks e.g. using mxsfb with the nwl bridge and mipi panels.
> > > > 
> > > > Fixes: b776b0f00f24 ("drm: mxsfb: Use bus_format from the nearest bridge if present")
> > > > 
> > > > Signed-off-by: Guido Günther <agx@sigxcpu.org>
> > > > ---
> > > > 
> > > > I'll look at what needs to be done in nwl separately but this also
> > > > unbreaks other bridge seupts that don't to format negotiation yet.
> > > > 
> > > >   drivers/gpu/drm/mxsfb/mxsfb_kms.c | 2 ++
> > > >   1 file changed, 2 insertions(+)
> > > > 
> > > > diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > > > index af6c620adf6e..4ef94cf686b0 100644
> > > > --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > > > +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > > > @@ -369,6 +369,8 @@ static void mxsfb_crtc_atomic_enable(struct drm_crtc *crtc,
> > > >   			drm_atomic_get_new_bridge_state(state,
> > > >   							mxsfb->bridge);
> > > >   		bus_format = bridge_state->input_bus_cfg.format;
> > > > +		if (bus_format == MEDIA_BUS_FMT_FIXED)
> > > > +			bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> > > 
> > > Shouldn't the NWL bridge return the correct format ?
> > 
> > Yes it should and I'll send a separate patch for that but we currently
> > don't do anything meaningful at all if the bridge doesn't do format
> > negotiation and then fail setup in mxsfb_set_formats().
> > 
> > I think we should at least preserve the status quo (as we do with the
> > non bridge case in b776b0f00f24 too).
> > 
> > We could have a warning to spot drivers that don't do that yet and hence
> > the generic code returns MEDIA_BUS_FMT_FIXED.
> > 
> That sounds sensible. Using a default format if we don't know what to
> do is going to be a unpleasant surprise for those with a display
> pipeline that doesn't work with the default format. So please add a
> dev_warn when we are doing this fallback.
> 
> Also I would argue that the NWL fix is the patch that should go in the
> stable tree. This one should only be a additional safety net, so I
> would drop the Fixes tag.

Dropped and folded into the small series with other fixes needed to
get get the bus format propagated up from the panel.
Cheers,
 -- Guido

> 
> Regards,
> Lucas
>