linux-kernel - Re: [PATCH] drm/bridge: parade-ps8640: Link device to ensure suspend/resume order

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Message-ID: <3b0af96e-f833-5cd1-7725-5ec37faab9fb@collabora.com>
Date:   Tue, 4 Jan 2022 15:48:08 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Robert Foss <robert.foss@...aro.org>
Cc:     a.hajda@...sung.com, narmstrong@...libre.com,
        laurent.pinchart@...asonboard.com, jonas@...boo.se,
        jernej.skrabec@...il.com, airlied@...ux.ie, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, kernel@...labora.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: parade-ps8640: Link device to ensure
 suspend/resume order

Il 04/01/22 15:22, Robert Foss ha scritto:
> Hey AngeloGioacchino,
> 
> On Tue, 2 Nov 2021 at 14:08, AngeloGioacchino Del Regno
> <angelogioacchino.delregno@...labora.com> wrote:
>>
>> Entering suspend while the display attached to this bridge is still on
>> makes the resume sequence to resume the bridge first, display last:
>> when this happens, we get a timeout while resuming the bridge, as its
>> MCU will get stuck due to the display being unpowered.
>>
>> On the other hand, on mt8173-elm, closing the lid makes the display to
>> get powered off first, bridge last, so at resume time the sequence is
>> swapped (compared to the first example) and everything just works
>> as expected.
>>
>> Add a stateless device link to the DRM device that this bridge belongs
>> to, ensuring a correct resume sequence and solving the unability to
>> correctly resume bridge operation in the first mentioned example.
>>
>> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>> ---
>>   drivers/gpu/drm/bridge/parade-ps8640.c | 22 ++++++++++++++++++++--
>>   1 file changed, 20 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
>> index 45100edd745b..191cc196c9d1 100644
>> --- a/drivers/gpu/drm/bridge/parade-ps8640.c
>> +++ b/drivers/gpu/drm/bridge/parade-ps8640.c
>> @@ -100,6 +100,7 @@ struct ps8640 {
>>          struct regulator_bulk_data supplies[2];
>>          struct gpio_desc *gpio_reset;
>>          struct gpio_desc *gpio_powerdown;
>> +       struct device_link *link;
>>          bool powered;
>>   };
>>
>> @@ -460,10 +461,23 @@ static int ps8640_bridge_attach(struct drm_bridge *bridge,
>>                  goto err_aux_register;
>>          }
>>
>> +       ps_bridge->link = device_link_add(bridge->dev->dev, dev, DL_FLAG_STATELESS);
>> +       if (!ps_bridge->link) {
>> +               dev_err(dev, "failed to create device link");
>> +               ret = -EINVAL;
>> +               goto err_devlink;
>> +       }
>> +
>>          /* Attach the panel-bridge to the dsi bridge */
>> -       return drm_bridge_attach(bridge->encoder, ps_bridge->panel_bridge,
>> +       ret = drm_bridge_attach(bridge->encoder, ps_bridge->panel_bridge,
>>                                   &ps_bridge->bridge, flags);
>> +       if (ret)
>> +               goto err_bridge_attach;
>>
>> +err_bridge_attach:
>> +       device_link_del(ps_bridge->link);
>> +err_devlink:
>> +       drm_dp_aux_unregister(&ps_bridge->aux);
>>   err_aux_register:
>>          mipi_dsi_detach(dsi);
>>   err_dsi_attach:
>> @@ -473,7 +487,11 @@ static int ps8640_bridge_attach(struct drm_bridge *bridge,
>>
>>   static void ps8640_bridge_detach(struct drm_bridge *bridge)
>>   {
>> -       drm_dp_aux_unregister(&bridge_to_ps8640(bridge)->aux);
>> +       struct ps8640 *ps_bridge = bridge_to_ps8640(bridge);
>> +
>> +       drm_dp_aux_unregister(&ps_bridge->aux);
>> +       if (ps_bridge->link)
>> +               device_link_del(ps_bridge->link);
>>   }
>>
>>   static struct edid *ps8640_bridge_get_edid(struct drm_bridge *bridge,
>> --
>> 2.33.1
>>
> 
> This patch does not apply on drm-misc-next, could you rebase it on the
> current branch?
> 

Sure, I'll rebase it asap.