[PATCH] drm/bridge: dw-hdmi: use safe format when first in bridge chain

[PATCH] drm/bridge: dw-hdmi: use safe format when first in bridge chain

[Neil Armstrong]

When the dw-hdmi bridge is in first place of the bridge chain, this
means there is now way to select an input format of the dw-hdmi HW
component.

Since introduction of display-connector, negociation was broken since
the dw-hdmi negociation code only worked when the dw-hdmi bridge was
in last position of the bridge chain or behind another bridge also
supporting input & output format negociation.

Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks")
was introduced to make negociation work again by making display-connector
act as a pass-through concerning input & output format negociation.

But in the case were the dw-hdmi was single in the bridge chain, for
example on Renesas SoCs, with the disply-connector bridge the dw-hdmi
is no more single, breaking output format.

Reported-by: Biju Das <biju.das.jz@bp.renesas.com>
Bisected-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Fixes: 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks").
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index 54d8fdad395f..9f2e1cac0ae2 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -2551,8 +2551,9 @@ static u32 *dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
 	if (!output_fmts)
 		return NULL;
 
-	/* If dw-hdmi is the only bridge, avoid negociating with ourselves */
-	if (list_is_singular(&bridge->encoder->bridge_chain)) {
+	/* If dw-hdmi is the first or only bridge, avoid negociating with ourselves */
+	if (list_is_singular(&bridge->encoder->bridge_chain) ||
+	    list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain)) {
 		*num_output_fmts = 1;
 		output_fmts[0] = MEDIA_BUS_FMT_FIXED;
 
@@ -2673,6 +2674,10 @@ static u32 *dw_hdmi_bridge_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
 	if (!input_fmts)
 		return NULL;
 
+	/* If dw-hdmi is the first bridge fall-back to safe output format */
+	if (list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain))
+		output_fmt = MEDIA_BUS_FMT_FIXED;
+
 	switch (output_fmt) {
 	/* If MEDIA_BUS_FMT_FIXED is tested, return default bus format */
 	case MEDIA_BUS_FMT_FIXED:
-- 
2.25.1

RE: [PATCH] drm/bridge: dw-hdmi: use safe format when first in bridge chain

[Biju Das]

Hi Neil,

Thanks for the patch

> Subject: [PATCH] drm/bridge: dw-hdmi: use safe format when first in bridge
> chain
> 
> When the dw-hdmi bridge is in first place of the bridge chain, this means
> there is now way to select an input format of the dw-hdmi HW component.
> 
> Since introduction of display-connector, negociation was broken since the
> dw-hdmi negociation code only worked when the dw-hdmi bridge was in last
> position of the bridge chain or behind another bridge also supporting
> input & output format negociation.
> 
> Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts
> callbacks") was introduced to make negociation work again by making
> display-connector act as a pass-through concerning input & output format
> negociation.
> 
> But in the case were the dw-hdmi was single in the bridge chain, for
> example on Renesas SoCs, with the disply-connector bridge the dw-hdmi is
> no more single, breaking output format.
> 
> Reported-by: Biju Das <biju.das.jz@bp.renesas.com>
> Bisected-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
> Tested-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
> Fixes: 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts
> callbacks").
> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> index 54d8fdad395f..9f2e1cac0ae2 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> @@ -2551,8 +2551,9 @@ static u32
> *dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
>  	if (!output_fmts)
>  		return NULL;
> 
> -	/* If dw-hdmi is the only bridge, avoid negociating with ourselves
> */
> -	if (list_is_singular(&bridge->encoder->bridge_chain)) {
> +	/* If dw-hdmi is the first or only bridge, avoid negociating with
> ourselves */
> +	if (list_is_singular(&bridge->encoder->bridge_chain) ||
> +	    list_is_first(&bridge->chain_node,
> +&bridge->encoder->bridge_chain)) {
>  		*num_output_fmts = 1;
>  		output_fmts[0] = MEDIA_BUS_FMT_FIXED;
> 
> @@ -2673,6 +2674,10 @@ static u32
> *dw_hdmi_bridge_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
>  	if (!input_fmts)
>  		return NULL;
> 
> +	/* If dw-hdmi is the first bridge fall-back to safe output format */
> +	if (list_is_first(&bridge->chain_node, &bridge->encoder-
> >bridge_chain))
> +		output_fmt = MEDIA_BUS_FMT_FIXED;
> +

Based on my debugging, this looks redundant, as get_output_bus_fmts already sets output_fmt = MEDIA_BUS_FMT_FIXED,
And *num_output_fmts = 1, so the function parameter output_fmt in input_bus_fmts will have MEDIA_BUS_FMT_FIXED
And no need to override output_fmt value.  I may be wrong here.

Regards,
Biju

>  	switch (output_fmt) {
>  	/* If MEDIA_BUS_FMT_FIXED is tested, return default bus format */
>  	case MEDIA_BUS_FMT_FIXED:
> --
> 2.25.1

Re: [PATCH] drm/bridge: dw-hdmi: use safe format when first in bridge chain

[Neil Armstrong]

On 17/01/2022 15:27, Biju Das wrote:
> Hi Neil,
> 
> Thanks for the patch
> 
>> Subject: [PATCH] drm/bridge: dw-hdmi: use safe format when first in bridge
>> chain
>>
>> When the dw-hdmi bridge is in first place of the bridge chain, this means
>> there is now way to select an input format of the dw-hdmi HW component.
>>
>> Since introduction of display-connector, negociation was broken since the
>> dw-hdmi negociation code only worked when the dw-hdmi bridge was in last
>> position of the bridge chain or behind another bridge also supporting
>> input & output format negociation.
>>
>> Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts
>> callbacks") was introduced to make negociation work again by making
>> display-connector act as a pass-through concerning input & output format
>> negociation.
>>
>> But in the case were the dw-hdmi was single in the bridge chain, for
>> example on Renesas SoCs, with the disply-connector bridge the dw-hdmi is
>> no more single, breaking output format.
>>
>> Reported-by: Biju Das <biju.das.jz@bp.renesas.com>
>> Bisected-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
>> Tested-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
>> Fixes: 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts
>> callbacks").
>> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
>> ---
>>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> index 54d8fdad395f..9f2e1cac0ae2 100644
>> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> @@ -2551,8 +2551,9 @@ static u32
>> *dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
>>  	if (!output_fmts)
>>  		return NULL;
>>
>> -	/* If dw-hdmi is the only bridge, avoid negociating with ourselves
>> */
>> -	if (list_is_singular(&bridge->encoder->bridge_chain)) {
>> +	/* If dw-hdmi is the first or only bridge, avoid negociating with
>> ourselves */
>> +	if (list_is_singular(&bridge->encoder->bridge_chain) ||
>> +	    list_is_first(&bridge->chain_node,
>> +&bridge->encoder->bridge_chain)) {
>>  		*num_output_fmts = 1;
>>  		output_fmts[0] = MEDIA_BUS_FMT_FIXED;
>>
>> @@ -2673,6 +2674,10 @@ static u32
>> *dw_hdmi_bridge_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
>>  	if (!input_fmts)
>>  		return NULL;
>>
>> +	/* If dw-hdmi is the first bridge fall-back to safe output format */
>> +	if (list_is_first(&bridge->chain_node, &bridge->encoder-
>>> bridge_chain))
>> +		output_fmt = MEDIA_BUS_FMT_FIXED;
>> +
> 
> Based on my debugging, this looks redundant, as get_output_bus_fmts already sets output_fmt = MEDIA_BUS_FMT_FIXED,
> And *num_output_fmts = 1, so the function parameter output_fmt in input_bus_fmts will have MEDIA_BUS_FMT_FIXED
> And no need to override output_fmt value.  I may be wrong here.

You're right, I added this in case another bridge than display-connector is used, but in fact it should instead
check if first bridge of the chain and output_fmt == MEDIA_BUS_FMT_RGB888_1X24 || output_fmt == MEDIA_BUS_FMT_FIXED
otherwise return an error.

I'll send it separately since it's out of the scope of the issue fixed.

Neil

> 
> Regards,
> Biju
> 
>>  	switch (output_fmt) {
>>  	/* If MEDIA_BUS_FMT_FIXED is tested, return default bus format */
>>  	case MEDIA_BUS_FMT_FIXED:
>> --
>> 2.25.1
> 

Re: [PATCH] drm/bridge: dw-hdmi: use safe format when first in bridge chain

[Marcel Ziswiler]

Hi Neil

Sorry, just some trivial spelling fixes.

On Mon, 2022-01-17 at 15:17 +0100, Neil Armstrong wrote:
> When the dw-hdmi bridge is in first place of the bridge chain, this
> means there is now way

no way

> to select an input format of the dw-hdmi HW
> component.
> 
> Since introduction of display-connector, negociation

:%s/negociation/negotiation/g

> was broken since
> the dw-hdmi negociation code only worked when the dw-hdmi bridge was
> in last position of the bridge chain or behind another bridge also
> supporting input & output format negociation.
> 
> Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks")
> was introduced to make negociation work again by making display-connector
> act as a pass-through concerning input & output format negociation.
> 
> But in the case were

where

> the dw-hdmi was single in the bridge chain, for
> example on Renesas SoCs, with the disply-connector

display-connector

> bridge the dw-hdmi
> is no more single, breaking output format.
> 
> Reported-by: Biju Das <biju.das.jz@bp.renesas.com>
> Bisected-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
> Tested-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
> Fixes: 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks").
> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> index 54d8fdad395f..9f2e1cac0ae2 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> @@ -2551,8 +2551,9 @@ static u32 *dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
>         if (!output_fmts)
>                 return NULL;
>  
> -       /* If dw-hdmi is the only bridge, avoid negociating with ourselves */
> -       if (list_is_singular(&bridge->encoder->bridge_chain)) {
> +       /* If dw-hdmi is the first or only bridge, avoid negociating with ourselves */
> +       if (list_is_singular(&bridge->encoder->bridge_chain) ||
> +           list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain)) {
>                 *num_output_fmts = 1;
>                 output_fmts[0] = MEDIA_BUS_FMT_FIXED;
>  
> @@ -2673,6 +2674,10 @@ static u32 *dw_hdmi_bridge_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
>         if (!input_fmts)
>                 return NULL;
>  
> +       /* If dw-hdmi is the first bridge fall-back to safe output format */
> +       if (list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain))
> +               output_fmt = MEDIA_BUS_FMT_FIXED;
> +
>         switch (output_fmt) {
>         /* If MEDIA_BUS_FMT_FIXED is tested, return default bus format */
>         case MEDIA_BUS_FMT_FIXED:

Cheers

Marcel

Re: [PATCH] drm/bridge: dw-hdmi: use safe format when first in bridge chain

[Neil Armstrong]

Hi,

On 17/01/2022 17:53, Marcel Ziswiler wrote:
> Hi Neil
> 
> Sorry, just some trivial spelling fixes.
> 
> On Mon, 2022-01-17 at 15:17 +0100, Neil Armstrong wrote:
>> When the dw-hdmi bridge is in first place of the bridge chain, this
>> means there is now way
> 
> no way
> 
>> to select an input format of the dw-hdmi HW
>> component.
>>
>> Since introduction of display-connector, negociation
> 
> :%s/negociation/negotiation/g
> 
>> was broken since
>> the dw-hdmi negociation code only worked when the dw-hdmi bridge was
>> in last position of the bridge chain or behind another bridge also
>> supporting input & output format negociation.
>>
>> Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks")
>> was introduced to make negociation work again by making display-connector
>> act as a pass-through concerning input & output format negociation.
>>
>> But in the case were
> 
> where
> 
>> the dw-hdmi was single in the bridge chain, for
>> example on Renesas SoCs, with the disply-connector
> 
> display-connector
> 
>> bridge the dw-hdmi
>> is no more single, breaking output format.
>>
>> Reported-by: Biju Das <biju.das.jz@bp.renesas.com>
>> Bisected-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
>> Tested-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
>> Fixes: 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks").
>> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
>> ---
>>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> index 54d8fdad395f..9f2e1cac0ae2 100644
>> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> @@ -2551,8 +2551,9 @@ static u32 *dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
>>         if (!output_fmts)
>>                 return NULL;
>>  
>> -       /* If dw-hdmi is the only bridge, avoid negociating with ourselves */
>> -       if (list_is_singular(&bridge->encoder->bridge_chain)) {
>> +       /* If dw-hdmi is the first or only bridge, avoid negociating with ourselves */
>> +       if (list_is_singular(&bridge->encoder->bridge_chain) ||
>> +           list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain)) {
>>                 *num_output_fmts = 1;
>>                 output_fmts[0] = MEDIA_BUS_FMT_FIXED;
>>  
>> @@ -2673,6 +2674,10 @@ static u32 *dw_hdmi_bridge_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
>>         if (!input_fmts)
>>                 return NULL;
>>  
>> +       /* If dw-hdmi is the first bridge fall-back to safe output format */
>> +       if (list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain))
>> +               output_fmt = MEDIA_BUS_FMT_FIXED;
>> +
>>         switch (output_fmt) {
>>         /* If MEDIA_BUS_FMT_FIXED is tested, return default bus format */
>>         case MEDIA_BUS_FMT_FIXED:
> 
> Cheers
> 
> Marcel
> 

Thanks for the spelling fixes,

Neil