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

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 13/10/2022 11:05, Thomas Zimmermann wrote:
Hi

Am 13.10.22 um 10:29 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.

Fixes: 2dd040946ecf ("drm/mgag200: Store values (not bits) in struct mgag200_pll_values")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jocelyn Falempe <jfalempe@xxxxxxxxxx>
---
  drivers/gpu/drm/mgag200/mgag200_g200se.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/mgag200/mgag200_g200se.c b/drivers/gpu/drm/mgag200/mgag200_g200se.c
index be389ed91cbd..4ec035029b8b 100644
--- a/drivers/gpu/drm/mgag200/mgag200_g200se.c
+++ b/drivers/gpu/drm/mgag200/mgag200_g200se.c
@@ -284,7 +284,7 @@ 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);
+    xpixpllcm = pixpllcm | BIT(7);

Thanks for figuring this out. G200SE apparently is special compared to the other models. The old MGA docs only list this bit as <reserved>. Really makes me wonder why this is different.

I think it might be because of the "clock * 2" trick for this model.
(so N parameter is half of what it should be, and doesn't have BIT(8) set). But I don't have the G200SE A specific hardware spec either.



Please write it as

   BIT(7) | pixpllcm

so that bit settings are ordered MSB-to-LSB and include a one-line comment that says that G200SE needs to set this bit unconditionally.

Thanks, I will send a v2 shortly.


Best regards
Thomas



      xpixpllcn = pixpllcn;
      xpixpllcp = (pixpllcs << 3) | pixpllcp;





[Index of Archives]     [Linux Kernel]     [Kernel Development Newbies]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Hiking]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux