[PATCH v2 2/7] drm: rcar-du: lvds: Add runtime PM

[Tomi Valkeinen]

On 20/01/2023 18:16, Laurent Pinchart wrote:
> Hi Tomi,
> 
> Thank you for the patch.
> 
> On Fri, Jan 20, 2023 at 10:50:04AM +0200, Tomi Valkeinen wrote:
>> Add simple runtime PM suspend and resume functionality.
> 
> I think you need to depend on PM in Kconfig. That's not a compile-time
> dependency but a runtime-dependency, with runtime PM support the
> suspend/resume handler will never be called.

Yes, LVDS won't work without runtime PM after this patch.

>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas at ideasonboard.com>
>> ---
>>   drivers/gpu/drm/rcar-du/rcar_lvds.c | 43 +++++++++++++++++++++++++----
>>   1 file changed, 37 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/rcar-du/rcar_lvds.c b/drivers/gpu/drm/rcar-du/rcar_lvds.c
>> index 81a060c2fe3f..8e1be51fbee6 100644
>> --- a/drivers/gpu/drm/rcar-du/rcar_lvds.c
>> +++ b/drivers/gpu/drm/rcar-du/rcar_lvds.c
>> @@ -16,6 +16,7 @@
>>   #include <linux/of_device.h>
>>   #include <linux/of_graph.h>
>>   #include <linux/platform_device.h>
>> +#include <linux/pm_runtime.h>
>>   #include <linux/slab.h>
>>   #include <linux/sys_soc.h>
>>   
>> @@ -316,8 +317,8 @@ int rcar_lvds_pclk_enable(struct drm_bridge *bridge, unsigned long freq)
>>   
>>   	dev_dbg(lvds->dev, "enabling LVDS PLL, freq=%luHz\n", freq);
>>   
>> -	ret = clk_prepare_enable(lvds->clocks.mod);
>> -	if (ret < 0)
>> +	ret = pm_runtime_resume_and_get(lvds->dev);
>> +	if (ret)
>>   		return ret;
>>   
>>   	__rcar_lvds_pll_setup_d3_e3(lvds, freq, true);
>> @@ -337,7 +338,7 @@ void rcar_lvds_pclk_disable(struct drm_bridge *bridge)
>>   
>>   	rcar_lvds_write(lvds, LVDPLLCR, 0);
>>   
>> -	clk_disable_unprepare(lvds->clocks.mod);
>> +	pm_runtime_put(lvds->dev);
> 
> Should we use pm_runtime_put_sync() here, to make sure the clock gets
> disabled right away ? The DU hardware may depend on the exact sequencing
> of events. I would then do the same in rcar_lvds_atomic_disable().

That's perhaps a good idea. I think I saw some of the docs saying that 
startup sequences must begin with the reset. If we don't use _sync, we 
could end up not resetting at all.

> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

Thanks!

  Tomi