[PATCH v2] drm/mgag200: Fix PLL setup for G200_SE_A rev >=4

[Jocelyn Falempe]

I just pushed it to drm-misc-next.

I also fixed the commit message a bit, the commit moving this line of 
code is in fact:

commit 877507bb954e ("drm/mgag200: Provide per-device callbacks for 
PIXPLLC")

Best Regards

-- 

Jocelyn

On 13/10/2022 15:55, Thomas Zimmermann wrote:
> 
> 
> Am 13.10.22 um 15:28 schrieb Jocelyn Falempe:
>> For G200_SE_A, PLL M setting is wrong, which leads to blank screen,
>> or "signal out of range" on VGA display.
>> previous code had "m |= 0x80" which was changed to
>> m |= ((pixpllcn & BIT(8)) >> 1);
>>
>> Tested on G200_SE_A rev 42
>>
>> This line of code was moved to another file with
>> commit 85397f6bc4ff ("drm/mgag200: Initialize each model in separate
>> function") but can be easily backported before this commit.
>>
>> v2: * put BIT(7) First to respect MSB-to-LSB (Thomas)
>>      * Add a comment to explain that this bit must be set (Thomas)
>>
>> Fixes: 2dd040946ecf ("drm/mgag200: Store values (not bits) in struct 
>> mgag200_pll_values")
>> Cc: stable at vger.kernel.org
>> Signed-off-by: Jocelyn Falempe <jfalempe at redhat.com>
> 
> Reviewed-by: Thomas Zimmermann <tzimmermann at suse.de>
> 
>> ---
>>   drivers/gpu/drm/mgag200/mgag200_g200se.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/mgag200/mgag200_g200se.c 
>> b/drivers/gpu/drm/mgag200/mgag200_g200se.c
>> index be389ed91cbd..bd6e573c9a1a 100644
>> --- a/drivers/gpu/drm/mgag200/mgag200_g200se.c
>> +++ b/drivers/gpu/drm/mgag200/mgag200_g200se.c
>> @@ -284,7 +284,8 @@ static void 
>> mgag200_g200se_04_pixpllc_atomic_update(struct drm_crtc *crtc,
>>       pixpllcp = pixpllc->p - 1;
>>       pixpllcs = pixpllc->s;
>> -    xpixpllcm = pixpllcm | ((pixpllcn & BIT(8)) >> 1);
>> +    // For G200SE A, BIT(7) should be set unconditionally.
>> +    xpixpllcm = BIT(7) | pixpllcm;
>>       xpixpllcn = pixpllcn;
>>       xpixpllcp = (pixpllcs << 3) | pixpllcp;
>