[PATCHv3 05/30] drm/omap: improve DPI clock selection on DRA7xx

[Tomi Valkeinen]

On 29/03/17 11:19, Laurent Pinchart wrote:
> Hi Tomi,
> 
> Thank you for the patch.
> 
> On Tuesday 28 Mar 2017 16:07:51 Tomi Valkeinen wrote:
>> The clock source selection for the LCD outputs is too hardcoded at the
>> moment. For example, LCD3 is set to use PLL2_1, and PLL2 doesn't exist
>> on DRA72x SoCs.
>>
>> There are quite many ways to configure the clocks, even using HDMI PLL
>> for LCD outputs, but enabling full configuration of the clocks is rather
>> tricky.
>>
>> This patch improves the situation a bit by checking if the PLL about to
>> be used exists, and if not, tries another one.
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
>> ---
>>  drivers/gpu/drm/omapdrm/dss/dpi.c | 47 +++++++++++++++++++++++++++---------
>>  1 file changed, 37 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/omapdrm/dss/dpi.c
>> b/drivers/gpu/drm/omapdrm/dss/dpi.c index e0b0c5c24c55..0f32d5d078c6 100644
>> --- a/drivers/gpu/drm/omapdrm/dss/dpi.c
>> +++ b/drivers/gpu/drm/omapdrm/dss/dpi.c
>> @@ -67,6 +67,42 @@ static struct dpi_data *dpi_get_data_from_pdev(struct
>> platform_device *pdev) return dev_get_drvdata(&pdev->dev);
>>  }
>>
>> +static enum dss_clk_source dpi_get_clk_src_dra7xx(enum omap_channel
>> channel)
>> +{
>> +	/*
>> +	 * Possible clock sources:
>> +	 * LCD1: FCK/PLL1_1/HDMI_PLL
>> +	 * LCD2: FCK/PLL1_3/HDMI_PLL (DRA74x: PLL2_3)
>> +	 * LCD3: FCK/PLL1_3/HDMI_PLL (DRA74x: PLL2_1)
>> +	 */
>> +
>> +	switch (channel) {
>> +	case OMAP_DSS_CHANNEL_LCD:
>> +	{
>> +		if (dss_pll_find_by_src(DSS_CLK_SRC_PLL1_1))
>> +			return DSS_CLK_SRC_PLL1_1;
>> +	}
> 
> Aren't you missing break statements ?

Huh, indeed I am. Thanks! Interesting that we've never hit that bug
(this has been in TI kernel for some time).

> 
>> +	case OMAP_DSS_CHANNEL_LCD2:
>> +	{
>> +		if (dss_pll_find_by_src(DSS_CLK_SRC_PLL1_3))
>> +			return DSS_CLK_SRC_PLL1_3;
>> +		if (dss_pll_find_by_src(DSS_CLK_SRC_PLL2_3))
>> +			return DSS_CLK_SRC_PLL2_3;
>> +	}
>> +	case OMAP_DSS_CHANNEL_LCD3:
>> +	{
>> +		if (dss_pll_find_by_src(DSS_CLK_SRC_PLL2_1))
>> +			return DSS_CLK_SRC_PLL2_1;
>> +		if (dss_pll_find_by_src(DSS_CLK_SRC_PLL1_3))
>> +			return DSS_CLK_SRC_PLL1_3;
> 
> What happens if LCD2 is already using PLL1_3 ?

Bad things, I guess? =)

It is a limitation with the current implementation that some
combinations are not really possible. To support all the cases, we
should somehow share the clocks, and manage the needs of the displays
using the same clocks... We have nothing for that.

So if you design a board that uses LCD2 and LCD3, and you don't have
PLL2, then the driver won't work.

Sharing the clock with two displays of exact same pixel clock possibly
works even now, but I have not tested it.

This patch improves the situation a bit, by allowing all cases where we
don't share the clocks, but it doesn't try to fix the sharing problem.

 Tomi

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