linux-kernel - Re: [PATCH v2 3/3] drm/panel: simple: add CMT430B19N00 LCD panel support

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Message-ID: <ee36a60d-5b65-4eb8-ac41-e4b6be1cf81f@bootlin.com>
Date: Tue, 5 Mar 2024 10:46:55 +0100
From: Jérémie Dautheribes
 <jeremie.dautheribes@...tlin.com>
To: Maxime Ripard <mripard@...nel.org>
Cc: Neil Armstrong <neil.armstrong@...aro.org>,
 Jessica Zhang <quic_jesszhan@...cinc.com>, Sam Ravnborg <sam@...nborg.org>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Daniel Vetter <daniel@...ll.ch>, Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Thierry Reding
 <thierry.reding@...il.com>, dri-devel@...ts.freedesktop.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 Yen-Mei Goh <yen-mei.goh@...sight.com>
Subject: Re: [PATCH v2 3/3] drm/panel: simple: add CMT430B19N00 LCD panel
 support

Hi Maxime,

On 04/03/2024 17:25, Maxime Ripard wrote:
> Hi,
> 
> On Mon, Mar 04, 2024 at 05:04:54PM +0100, Jérémie Dautheribes wrote:
>> Add support for Crystal Clear Technology CMT430B19N00 4.3" 480x272
>> TFT-LCD panel.
>>
>> Signed-off-by: Jérémie Dautheribes <jeremie.dautheribes@...tlin.com>
>> ---
>>   drivers/gpu/drm/panel/panel-simple.c | 29 ++++++++++++++++++++++++++++
>>   1 file changed, 29 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
>> index 20e3df1c59d4..b940220f56e2 100644
>> --- a/drivers/gpu/drm/panel/panel-simple.c
>> +++ b/drivers/gpu/drm/panel/panel-simple.c
>> @@ -1457,6 +1457,32 @@ static const struct panel_desc boe_hv070wsa = {
>>   	.connector_type = DRM_MODE_CONNECTOR_LVDS,
>>   };
>>   
>> +static const struct drm_display_mode cct_cmt430b19n00_mode = {
>> +	.clock = 9000,
>> +	.hdisplay = 480,
>> +	.hsync_start = 480 + 43,
>> +	.hsync_end = 480 + 43 + 8,
>> +	.htotal = 480 + 43 + 8 + 4,
>> +	.vdisplay = 272,
>> +	.vsync_start = 272 + 12,
>> +	.vsync_end = 272 + 12 + 8,
>> +	.vtotal = 272 + 12 + 8 + 4,
>> +	.flags = DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC,
>> +};
> 
> Your pixel clock doesn't really match the rest of the timings:
> 
> (480 + 43 + 8 + 4) * (272 + 12 + 8 + 4) * 60 = 9501600
> 
> So a ~6% deviation.
> 
> What does the datasheet say?

Indeed it does not exactly match but the datasheet indicates that the 
typical clock frequency is 9MHz and when this frequency is used, the 
typical values of the other parameters are those we have defined in the 
drm_display_mode structure. I don't see any information about the 
accepted deviation either.

Best regards,

Jérémie