[PATCH] drm/panel: Set max rate for Ilitek ILI9881C

[Andrzej Hajda]

On 14.11.2018 16:14, Andrzej Hajda wrote:
> On 14.11.2018 12:17, Linus Walleij wrote:
>> After adding the hs_rate and lp_rate fields to the DSI device
>> we need to populate these accordingly so display drivers can
>> respect them.
>>
>> This figure for HS rate comes from the ILI9881C manual, the
>> calculation is explained in the comment.
>>
>> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>> Cc: Andrzej Hajda <a.hajda at samsung.com>
>> Cc: Maxime Ripard <maxime.ripard at bootlin.com>
>> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
>> ---
>>  drivers/gpu/drm/panel/panel-ilitek-ili9881c.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c b/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
>> index 3ad4a46c4e94..f58250f84f8c 100644
>> --- a/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
>> +++ b/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
>> @@ -465,6 +465,13 @@ static int ili9881c_dsi_probe(struct mipi_dsi_device *dsi)
>>  	dsi->mode_flags = MIPI_DSI_MODE_VIDEO_SYNC_PULSE;
>>  	dsi->format = MIPI_DSI_FMT_RGB888;
>>  	dsi->lanes = 4;
>> +	/*
>> +	 * The datasheet (table 39) specifies "limited clock channel speed"
>> +	 * for 4 lanes as 550 Mbps for RGB888. As this is 4 bits at the time,
>> +	 * the maximum HS frequency is 550/4 = 137.5 MHz.
>> +	 */
>> +	dsi->hs_rate = 137500000;
>> +	/* FIXME: LP max rate does not seem to be specified */
>>  
>>  	return mipi_dsi_attach(dsi);
>>  }
> Table 42 says: "Length of LP-00, LP-01, LP-10 or LP-11 periods": min
> 50ns, max 75ns.
>
> 1/50ns = max LPM rate = 20.000.000Hz

...and since in LP transmission there are two periods per bit it should
be divided by 2.

So max LPM rate shall be 10.000.000Hz - anyway it would be good if
somebody verifies it.


Regards

Andrzej


>
>
> Regards
>
> Andrzej
>
>
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