[AMD Public Use] Hello Christian, Yes, that 100 is hardcoded in Radeon, and git blame says it was one of your patches which made it 100 from 128 😊. Would you mind having a look at commit id: 4b21ce1b4b5d262e7d4656b8ececc891fc3cb806 ? Regards Shashank -----Original Message----- From: Koenig, Christian <Christian.Koenig@xxxxxxx> Sent: Wednesday, November 4, 2020 3:35 PM To: Sharma, Shashank <Shashank.Sharma@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx Cc: Deucher, Alexander <Alexander.Deucher@xxxxxxx>; Qin, Eddy <Eddy.Qin@xxxxxxx> Subject: Re: [PATCH] drm/amdgpu: clip the ref divider max value at 100 Am 03.11.20 um 18:13 schrieb Shashank Sharma: > This patch limits the ref_div_max value to 100, during the calculation > of PLL feedback reference divider. With current value (128), the > produced fb_ref_div value generates unstable output at particular > frequencies. Radeon driver limits this value at 100. Mhm, is that 100 hard coded in radeon? I have no idea where that is coming from. Best would probably to grab a hardware engineer and try to figure out what the real maximums for the PLL is to still produce a stable signal. Christian. > > On Oland, when we try to setup mode 2048x1280@60 (a bit weird, I > know), it demands a clock of 221270 Khz. It's been observed that the > PLL calculations using values 128 and 100 are vastly different, and > look like this: > > +------------------------------------------+ > |Parameter |AMDGPU |Radeon | > | | | | > +-------------+----------------------------+ > |Clock feedback | | > |divider max | 128 | 100 | > |cap value | | | > | | | | > | | | | > +------------------------------------------+ > |ref_div_max | | | > | | 42 | 20 | > | | | | > | | | | > +------------------------------------------+ > |ref_div | 42 | 20 | > | | | | > +------------------------------------------+ > |fb_div | 10326 | 8195 | > +------------------------------------------+ > |fb_div | 1024 | 163 | > +------------------------------------------+ > |fb_dev_p | 4 | 9 | > |frac fb_de^_p| | | > +----------------------------+-------------+ > > With ref_div_max value clipped at 100, AMDGPU driver can also drive > videmode 2048x1280@60 (221Mhz) and produce proper output without any > blanking and distortion on the screen. > > PS: This value was changed from 128 to 100 in Radeon driver also, here: > https://github.com/freedesktop/drm-tip/commit/4b21ce1b4b5d262e7d4656b8 > ececc891fc3cb806 > > Cc: Alex Deucher <Alexander.Deucher@xxxxxxx> > Cc: Christian König <christian.koenig@xxxxxxx> > Cc: Eddy Qin <Eddy.Qin@xxxxxxx> > > Signed-off-by: Shashank Sharma <shashank.sharma@xxxxxxx> > --- > drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c > b/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c > index 1f2305b7bd13..23a2e1ebf78a 100644 > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c > @@ -85,7 +85,7 @@ static void amdgpu_pll_get_fb_ref_div(unsigned nom, unsigned den, unsigned post_ > unsigned *fb_div, unsigned *ref_div) > { > /* limit reference * post divider to a maximum */ > - ref_div_max = min(128 / post_div, ref_div_max); > + ref_div_max = min(100 / post_div, ref_div_max); > > /* get matching reference and feedback divider */ > *ref_div = min(max(DIV_ROUND_CLOSEST(den, post_div), 1u), > ref_div_max); _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx
