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

[Yongxing Mou <quic_yongmou@quicinc.com>]

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.
>