[PATCH] drm/omap: change default signal polarities and drives

[Tomi Valkeinen]

On 17/04/2020 16:29, Laurent Pinchart wrote:
> Hi Tomi,
> 
> Thank you for the patch.
> 
> On Fri, Apr 17, 2020 at 02:41:51PM +0300, Tomi Valkeinen wrote:
>> If the given videomode does not specify DISPLAY_FLAG_* for the specific
>> signal property, the driver used a default value. These defaults were
>> never thought through, as the expectation was that all the DISPLAY_FLAGS
>> are always set explicitly.
>>
>> With DRM bridge and panel drivers this is not the case, and while that
>> issue should be resolved in the future, it's still good to have sane
>> signal defaults.
>>
>> This patch changes the defaults to what the hardware has as reset
>> defaults. Also, based on my experience, I think they make sense and are
>> more likely correct than the defaults without this patch.
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
>> ---
>>   drivers/gpu/drm/omapdrm/dss/dispc.c | 33 ++++++-----------------------
>>   1 file changed, 6 insertions(+), 27 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/omapdrm/dss/dispc.c b/drivers/gpu/drm/omapdrm/dss/dispc.c
>> index dbb90f2d2ccd..6639ee9b05d3 100644
>> --- a/drivers/gpu/drm/omapdrm/dss/dispc.c
>> +++ b/drivers/gpu/drm/omapdrm/dss/dispc.c
>> @@ -3137,33 +3137,12 @@ static void _dispc_mgr_set_lcd_timings(struct dispc_device *dispc,
>>   	dispc_write_reg(dispc, DISPC_TIMING_H(channel), timing_h);
>>   	dispc_write_reg(dispc, DISPC_TIMING_V(channel), timing_v);
>>   
>> -	if (vm->flags & DISPLAY_FLAGS_VSYNC_HIGH)
>> -		vs = false;
>> -	else
>> -		vs = true;
>> -
>> -	if (vm->flags & DISPLAY_FLAGS_HSYNC_HIGH)
>> -		hs = false;
>> -	else
>> -		hs = true;
>> -
>> -	if (vm->flags & DISPLAY_FLAGS_DE_HIGH)
>> -		de = false;
>> -	else
>> -		de = true;
>> -
>> -	if (vm->flags & DISPLAY_FLAGS_PIXDATA_POSEDGE)
>> -		ipc = false;
>> -	else
>> -		ipc = true;
>> -
>> -	/* always use the 'rf' setting */
>> -	onoff = true;
>> -
>> -	if (vm->flags & DISPLAY_FLAGS_SYNC_POSEDGE)
>> -		rf = true;
>> -	else
>> -		rf = false;
>> +	vs = !!(vm->flags & DISPLAY_FLAGS_VSYNC_LOW);
>> +	hs = !!(vm->flags & DISPLAY_FLAGS_HSYNC_LOW);
>> +	de = !!(vm->flags & DISPLAY_FLAGS_DE_LOW);
>> +	ipc = !!(vm->flags & DISPLAY_FLAGS_PIXDATA_NEGEDGE);
>> +	onoff = true; /* always use the 'rf' setting */
>> +	rf = !!(vm->flags & DISPLAY_FLAGS_SYNC_POSEDGE);
> 
> Would it make sense to WARN() if flags are not set, to catch offenders
> and fix them ? Apart from that,

Maybe at some point, but for now it would probably be printing WARNs on all boards. I haven't looked 
at exactly which driver combinations get the bus flags/formats right, but I have a feeling that it's 
not too many.

And some pieces of hardware also may be "don't care" for certain flags, so I think it's a valid case 
that a bridge/panel doesn't define some of the flags.

  Tomi

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