[PATCH v2] drm/bridge: dw-hdmi: use safe format when first in bridge chain

[PATCH v2] 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 no way to select an input format of the dw-hdmi HW
component.

Since introduction of display-connector, negotiation was broken since
the dw-hdmi negotiation 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 negotiation.

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

But in the case where the dw-hdmi is single in the bridge chain, for
example on Renesas SoCs, with the 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>
---
Changes since v1:
- Remove bad fix in dw_hdmi_bridge_atomic_get_input_bus_fmts
- Fix typos in commit message

 drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 5 +++--
 1 file changed, 3 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..97cdc61b57f6 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;
 
-- 
2.25.1

Re: [PATCH v2] drm/bridge: dw-hdmi: use safe format when first in bridge chain

[Jagan Teki]

On Wed, Jan 19, 2022 at 5:58 PM Neil Armstrong <narmstrong@baylibre.com> wrote:
>
> When the dw-hdmi bridge is in first place of the bridge chain, this
> means there is no way to select an input format of the dw-hdmi HW
> component.
>
> Since introduction of display-connector, negotiation was broken since
> the dw-hdmi negotiation 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 negotiation.
>
> Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks")
> was introduced to make negotiation work again by making display-connector
> act as a pass-through concerning input & output format negotiation.
>
> But in the case where the dw-hdmi is single in the bridge chain, for
> example on Renesas SoCs, with the 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>
> ---
> Changes since v1:
> - Remove bad fix in dw_hdmi_bridge_atomic_get_input_bus_fmts
> - Fix typos in commit message
>
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 5 +++--
>  1 file changed, 3 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..97cdc61b57f6 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)) {

What if we use bridge helper, drm_bridge_chain_get_first_bridge in
order to find the first bridge in chain?

Thanks,
Jagan.

Re: [PATCH v2] drm/bridge: dw-hdmi: use safe format when first in bridge chain

[Neil Armstrong]

Hi,

On 20/01/2022 12:14, Jagan Teki wrote:
> On Wed, Jan 19, 2022 at 5:58 PM Neil Armstrong <narmstrong@baylibre.com> wrote:
>>
>> When the dw-hdmi bridge is in first place of the bridge chain, this
>> means there is no way to select an input format of the dw-hdmi HW
>> component.
>>
>> Since introduction of display-connector, negotiation was broken since
>> the dw-hdmi negotiation 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 negotiation.
>>
>> Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks")
>> was introduced to make negotiation work again by making display-connector
>> act as a pass-through concerning input & output format negotiation.
>>
>> But in the case where the dw-hdmi is single in the bridge chain, for
>> example on Renesas SoCs, with the 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>
>> ---
>> Changes since v1:
>> - Remove bad fix in dw_hdmi_bridge_atomic_get_input_bus_fmts
>> - Fix typos in commit message
>>
>>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 5 +++--
>>  1 file changed, 3 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..97cdc61b57f6 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)) {
> 
> What if we use bridge helper, drm_bridge_chain_get_first_bridge in
> order to find the first bridge in chain?

drm_bridge_chain_get_first_bridge() would be similar, since we already access bridge_chain
in the previous check, it's simpler like that.

Neil

> 
> Thanks,
> Jagan.
> 

Re: [PATCH v2] drm/bridge: dw-hdmi: use safe format when first in bridge chain

[Neil Armstrong]

Hi,

On 19/01/2022 13:28, Neil Armstrong wrote:
> When the dw-hdmi bridge is in first place of the bridge chain, this
> means there is no way to select an input format of the dw-hdmi HW
> component.
> 
> Since introduction of display-connector, negotiation was broken since
> the dw-hdmi negotiation 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 negotiation.
> 
> Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks")
> was introduced to make negotiation work again by making display-connector
> act as a pass-through concerning input & output format negotiation.
> 
> But in the case where the dw-hdmi is single in the bridge chain, for
> example on Renesas SoCs, with the 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>
> ---
> Changes since v1:
> - Remove bad fix in dw_hdmi_bridge_atomic_get_input_bus_fmts
> - Fix typos in commit message
> 
>   drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 5 +++--
>   1 file changed, 3 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..97cdc61b57f6 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;
>   

Can a bridge reviewer get an eye on this ? this actually solves an issue reported on a Renesas platform.

Neil

Re: [PATCH v2] drm/bridge: dw-hdmi: use safe format when first in bridge chain

[Robert Foss]

On Wed, 19 Jan 2022 at 13:28, Neil Armstrong <narmstrong@baylibre.com> wrote:
>
> When the dw-hdmi bridge is in first place of the bridge chain, this
> means there is no way to select an input format of the dw-hdmi HW
> component.
>
> Since introduction of display-connector, negotiation was broken since
> the dw-hdmi negotiation 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 negotiation.
>
> Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks")

I think this is the wrong hash. Is 7cd70656d128 the actual hash?

> was introduced to make negotiation work again by making display-connector
> act as a pass-through concerning input & output format negotiation.
>
> But in the case where the dw-hdmi is single in the bridge chain, for
> example on Renesas SoCs, with the 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").

This hash too.

> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
> ---
> Changes since v1:
> - Remove bad fix in dw_hdmi_bridge_atomic_get_input_bus_fmts
> - Fix typos in commit message
>
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 5 +++--
>  1 file changed, 3 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..97cdc61b57f6 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;
>
> --
> 2.25.1
>

There are two checkstyle issues apart from the above mentioned hash
issues, and I think we can ignore those. With the above mentioned
issue fixed, feel free to add my r-b.

Reviewed-by: Robert Foss <robert.foss@linaro.org>

Re: [PATCH v2] drm/bridge: dw-hdmi: use safe format when first in bridge chain

[Neil Armstrong]

Hi,

On 04/02/2022 15:05, Robert Foss wrote:
> On Wed, 19 Jan 2022 at 13:28, Neil Armstrong <narmstrong@baylibre.com> wrote:
>>
>> When the dw-hdmi bridge is in first place of the bridge chain, this
>> means there is no way to select an input format of the dw-hdmi HW
>> component.
>>
>> Since introduction of display-connector, negotiation was broken since
>> the dw-hdmi negotiation 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 negotiation.
>>
>> Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks")
> 
> I think this is the wrong hash. Is 7cd70656d128 the actual hash?

Wow indeed, thanks for checking...

> 
>> was introduced to make negotiation work again by making display-connector
>> act as a pass-through concerning input & output format negotiation.
>>
>> But in the case where the dw-hdmi is single in the bridge chain, for
>> example on Renesas SoCs, with the 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").
> 
> This hash too.
> 
>> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
>> ---
>> Changes since v1:
>> - Remove bad fix in dw_hdmi_bridge_atomic_get_input_bus_fmts
>> - Fix typos in commit message
>>
>>   drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 5 +++--
>>   1 file changed, 3 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..97cdc61b57f6 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;
>>
>> --
>> 2.25.1
>>
> 
> There are two checkstyle issues apart from the above mentioned hash
> issues, and I think we can ignore those. With the above mentioned
> issue fixed, feel free to add my r-b.
> 
> Reviewed-by: Robert Foss <robert.foss@linaro.org>

Thanks, I'll fix & resend with your r-b.

Neil