Re: [PATCH v2 01/38] drm/msm/dp: split msm_dp_panel_read_sink_caps() into two parts and drop panel drm_edid

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On 27/06/2025 10:49, Yongxing Mou wrote:
> 
> 
> On 2025/6/25 21:32, Dmitry Baryshkov wrote:
>> On Wed, Jun 25, 2025 at 04:43:55PM +0800, Yongxing Mou wrote:
>>>
>>>
>>> On 2025/6/9 20:41, Dmitry Baryshkov wrote:
>>>> On Mon, Jun 09, 2025 at 08:21:20PM +0800, Yongxing Mou wrote:
>>>>> From: Abhinav Kumar <quic_abhinavk@quicinc.com>
>>>>>
>>>>> In preparation of DP MST where link caps are read for the
>>>>> immediate downstream device and the edid is read through
>>>>
>>>> EDID, not edid. Please review all your patches for up/down case.
>>>>
>>> Got it. Thanks~
>>>>> sideband messaging, split the msm_dp_panel_read_sink_caps() into
>>>>> two parts which read the link parameters and the edid parts
>>>>> respectively. Also drop the panel drm_edid cached as we actually
>>>>> don't need it.
>>>>
>>>> Also => separate change.
>>>>
>>> Got it.
>>>>>
>>>>> Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
>>>>> Signed-off-by: Yongxing Mou <quic_yongmou@quicinc.com>
>>>>> ---
>>>>>    drivers/gpu/drm/msm/dp/dp_display.c | 13 +++++----
>>>>>    drivers/gpu/drm/msm/dp/dp_panel.c   | 55 +++++++++++++++++++ 
>>>>> +-----------------
>>>>>    drivers/gpu/drm/msm/dp/dp_panel.h   |  6 ++--
>>>>>    3 files changed, 40 insertions(+), 34 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/ 
>>>>> msm/dp/dp_display.c
>>>>> index 
>>>>> 6f05a939ce9e648e9601597155999b6f85adfcff..4a9b65647cdef1ed6c3bb851f93df0db8be977af 100644
>>>>> --- a/drivers/gpu/drm/msm/dp/dp_display.c
>>>>> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
>>>>> @@ -389,7 +389,11 @@ static int 
>>>>> msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp)
>>>>>        dp->link->lttpr_count = msm_dp_display_lttpr_init(dp, dpcd);
>>>>> -    rc = msm_dp_panel_read_sink_caps(dp->panel, connector);
>>>>> +    rc = msm_dp_panel_read_link_caps(dp->panel);
>>>>> +    if (rc)
>>>>> +        goto end;
>>>>> +
>>>>> +    rc = msm_dp_panel_read_edid(dp->panel, connector);
>>>>>        if (rc)
>>>>>            goto end;
>>>>> @@ -720,7 +724,6 @@ static int msm_dp_irq_hpd_handle(struct 
>>>>> msm_dp_display_private *dp, u32 data)
>>>>>    static void msm_dp_display_deinit_sub_modules(struct 
>>>>> msm_dp_display_private *dp)
>>>>>    {
>>>>>        msm_dp_audio_put(dp->audio);
>>>>> -    msm_dp_panel_put(dp->panel);
>>>>>        msm_dp_aux_put(dp->aux);
>>>>>    }
>>>>> @@ -783,7 +786,7 @@ static int msm_dp_init_sub_modules(struct 
>>>>> msm_dp_display_private *dp)
>>>>>            rc = PTR_ERR(dp->ctrl);
>>>>>            DRM_ERROR("failed to initialize ctrl, rc = %d\n", rc);
>>>>>            dp->ctrl = NULL;
>>>>> -        goto error_ctrl;
>>>>> +        goto error_link;
>>>>>        }
>>>>>        dp->audio = msm_dp_audio_get(dp->msm_dp_display.pdev, dp- 
>>>>> >catalog);
>>>>> @@ -791,13 +794,11 @@ static int msm_dp_init_sub_modules(struct 
>>>>> msm_dp_display_private *dp)
>>>>>            rc = PTR_ERR(dp->audio);
>>>>>            pr_err("failed to initialize audio, rc = %d\n", rc);
>>>>>            dp->audio = NULL;
>>>>> -        goto error_ctrl;
>>>>> +        goto error_link;
>>>>>        }
>>>>>        return rc;
>>>>> -error_ctrl:
>>>>> -    msm_dp_panel_put(dp->panel);
>>>>>    error_link:
>>>>>        msm_dp_aux_put(dp->aux);
>>>>>    error:
>>>>> diff --git a/drivers/gpu/drm/msm/dp/dp_panel.c b/drivers/gpu/drm/ 
>>>>> msm/dp/dp_panel.c
>>>>> index 
>>>>> 4e8ab75c771b1e3a2d62f75e9993e1062118482b..d9041e235104a74b3cc50ff2e307eae0c4301ef3 100644
>>>>> --- a/drivers/gpu/drm/msm/dp/dp_panel.c
>>>>> +++ b/drivers/gpu/drm/msm/dp/dp_panel.c
>>>>> @@ -118,14 +118,13 @@ static u32 
>>>>> msm_dp_panel_get_supported_bpp(struct msm_dp_panel *msm_dp_panel,
>>>>>        return min_supported_bpp;
>>>>>    }
>>>>> -int msm_dp_panel_read_sink_caps(struct msm_dp_panel *msm_dp_panel,
>>>>> -    struct drm_connector *connector)
>>>>> +int msm_dp_panel_read_link_caps(struct msm_dp_panel *msm_dp_panel)
>>>>>    {
>>>>>        int rc, bw_code;
>>>>>        int count;
>>>>>        struct msm_dp_panel_private *panel;
>>>>> -    if (!msm_dp_panel || !connector) {
>>>>> +    if (!msm_dp_panel) {
>>>>>            DRM_ERROR("invalid input\n");
>>>>>            return -EINVAL;
>>>>>        }
>>>>> @@ -160,26 +159,29 @@ int msm_dp_panel_read_sink_caps(struct 
>>>>> msm_dp_panel *msm_dp_panel,
>>>>>        rc = drm_dp_read_downstream_info(panel->aux, msm_dp_panel- 
>>>>> >dpcd,
>>>>>                         msm_dp_panel->downstream_ports);
>>>>> -    if (rc)
>>>>> -        return rc;
>>>>> +    return rc;
>>>>> +}
>>>>> -    drm_edid_free(msm_dp_panel->drm_edid);
>>>>> +int msm_dp_panel_read_edid(struct msm_dp_panel *msm_dp_panel, 
>>>>> struct drm_connector *connector)
>>>>> +{
>>>>> +    struct msm_dp_panel_private *panel;
>>>>> +    const struct drm_edid *drm_edid;
>>>>> +
>>>>> +    panel = container_of(msm_dp_panel, struct 
>>>>> msm_dp_panel_private, msm_dp_panel);
>>>>> -    msm_dp_panel->drm_edid = drm_edid_read_ddc(connector, &panel- 
>>>>> >aux->ddc);
>>>>> +    drm_edid = drm_edid_read_ddc(connector, &panel->aux->ddc);
>>>>> -    drm_edid_connector_update(connector, msm_dp_panel->drm_edid);
>>>>> +    drm_edid_connector_update(connector, drm_edid);
>>>>> -    if (!msm_dp_panel->drm_edid) {
>>>>> +    if (!drm_edid) {
>>>>>            DRM_ERROR("panel edid read failed\n");
>>>>>            /* check edid read fail is due to unplug */
>>>>>            if (!msm_dp_catalog_link_is_connected(panel->catalog)) {
>>>>> -            rc = -ETIMEDOUT;
>>>>> -            goto end;
>>>>> +            return -ETIMEDOUT;
>>>>>            }
>>>>>        }
>>>>> -end:
>>>>> -    return rc;
>>>>> +    return 0;
>>>>>    }
>>>>>    u32 msm_dp_panel_get_mode_bpp(struct msm_dp_panel *msm_dp_panel,
>>>>> @@ -208,15 +210,20 @@ u32 msm_dp_panel_get_mode_bpp(struct 
>>>>> msm_dp_panel *msm_dp_panel,
>>>>>    int msm_dp_panel_get_modes(struct msm_dp_panel *msm_dp_panel,
>>>>>        struct drm_connector *connector)
>>>>>    {
>>>>> +    struct msm_dp_panel_private *panel;
>>>>> +    const struct drm_edid *drm_edid;
>>>>> +
>>>>>        if (!msm_dp_panel) {
>>>>>            DRM_ERROR("invalid input\n");
>>>>>            return -EINVAL;
>>>>>        }
>>>>> -    if (msm_dp_panel->drm_edid)
>>>>> -        return drm_edid_connector_add_modes(connector);
>>>>> +    panel = container_of(msm_dp_panel, struct 
>>>>> msm_dp_panel_private, msm_dp_panel);
>>>>> +
>>>>> +    drm_edid = drm_edid_read_ddc(connector, &panel->aux->ddc);
>>>>> +    drm_edid_connector_update(connector, drm_edid);
>>>>
>>>> If EDID has been read and processed after HPD high event, why do we 
>>>> need
>>>> to re-read it again? Are we expecting that EDID will change?
>>>>
>>> Here we indeed don't need to read the EDID again, so we can directly 
>>> call
>>> drm_edid_connector_add_modes. Thanks.
>>>>> -    return 0;
>>>>> +    return drm_edid_connector_add_modes(connector);
>>>>>    }
>>>>>    static u8 msm_dp_panel_get_edid_checksum(const struct edid *edid)
>>>>> @@ -229,6 +236,7 @@ static u8 msm_dp_panel_get_edid_checksum(const 
>>>>> struct edid *edid)
>>>>>    void msm_dp_panel_handle_sink_request(struct msm_dp_panel 
>>>>> *msm_dp_panel)
>>>>>    {
>>>>>        struct msm_dp_panel_private *panel;
>>>>> +    const struct drm_edid *drm_edid;
>>>>>        if (!msm_dp_panel) {
>>>>>            DRM_ERROR("invalid input\n");
>>>>> @@ -238,8 +246,13 @@ void msm_dp_panel_handle_sink_request(struct 
>>>>> msm_dp_panel *msm_dp_panel)
>>>>>        panel = container_of(msm_dp_panel, struct 
>>>>> msm_dp_panel_private, msm_dp_panel);
>>>>>        if (panel->link->sink_request & DP_TEST_LINK_EDID_READ) {
>>>>> +        drm_edid = drm_edid_read_ddc(msm_dp_panel->connector, 
>>>>> &panel->aux->ddc);
>>>>
>>>> And again....
>>>>
>>> Here we need the struct edid,since we drop the cached drm_edid, so we 
>>> need
>>> to read it again. Or we can return the drm_edid from 
>>> msm_dp_panel_read_edid
>>> and pass it to msm_dp_panel_handle_sink_request, then we don't need 
>>> to read
>>> drm_edid here. Emm, I'm still a bit curious why we can't cache the 
>>> drm_edid?
>>> It would help us to access it when needed. Emm, i see other drivers also
>>> cache it.
>>
>> Yes, they can cache EDID. However, in this case we don't even need it at
>> all. This piece needs to be rewritten to use
>> drm_dp_send_real_edid_checksum(), connector->real_edid_checksum.
>>
>> Corresponding changes can be submitted separately.
>>
> Got it, thanks, will separate this patch from MST patches..  Even if we 
> use drm_dp_send_real_edid_checksum to send connector- 
>  >real_edid_checksum, that’s only when the EDID state is incorrect.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/ 
> drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c?h=v6.16-rc3#n1020
>   When the EDID is read correctly, it should send edid->checksum instead.

I wonder if we should fix the drm_edid to always set real_edid_checksum 
instead.

>>
> 


-- 
With best wishes
Dmitry