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Sun, 28 Sep 2025 14:15:01 +0000 Message-ID: <221fd37b-e2a4-419c-9ac7-bb9eea0b4f78@amd.com> Date: Sun, 28 Sep 2025 16:14:56 +0200 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/3] drm/amd/display: Set stricter clock dividers on DCE 6-10 To: =?UTF-8?Q?Timur_Krist=C3=B3f?= , amd-gfx@lists.freedesktop.org Cc: alexander.deucher@amd.com, alex.hung@amd.com, harry.wentland@amd.com, siqueira@igalia.com References: <20250926182614.26629-1-timur.kristof@gmail.com> <20250926182614.26629-4-timur.kristof@gmail.com> Content-Language: en-US From: =?UTF-8?Q?Christian_K=C3=B6nig?= In-Reply-To: <20250926182614.26629-4-timur.kristof@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: BL0PR02CA0140.namprd02.prod.outlook.com (2603:10b6:208:35::45) To PH7PR12MB5685.namprd12.prod.outlook.com (2603:10b6:510:13c::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH7PR12MB5685:EE_|CYYPR12MB9015:EE_ X-MS-Office365-Filtering-Correlation-Id: 16c9b72f-c60f-47be-6b26-08ddfe996975 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7053199007; 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This makes it > more stable. > > The values here are taken from the non-DC code. There are also a bunch of other restrictions which need to be kept in mind. For example what is the minimum feedback divider value the DC code uses? We once had a longer discussion with the PLL HW engineers to get this working because at least the display code we used as reference back then got it wrong. Regards, Christian. > > Signed-off-by: Timur Kristóf > --- > drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c b/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c > index b4f5b4a6331a..00f25e2ee081 100644 > --- a/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c > +++ b/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c > @@ -1700,6 +1700,13 @@ bool dce110_clk_src_construct( > clk_src->cs_mask->PLL_POST_DIV_PIXCLK; > calc_pll_cs_init_data.min_pll_ref_divider = 1; > calc_pll_cs_init_data.max_pll_ref_divider = clk_src->cs_mask->PLL_REF_DIV; > + > + if (ctx->dce_version <= DCE_VERSION_10_0) { > + /* Set stricter dividers to stabilize the PLL's feedback loop on old HW. */ > + calc_pll_cs_init_data.min_pix_clk_pll_post_divider = 2; > + calc_pll_cs_init_data.min_pll_ref_divider = 2; > + } > + > /* when 0 use minInputPxlClkPLLFrequencyInKHz from firmwareInfo*/ > calc_pll_cs_init_data.min_override_input_pxl_clk_pll_freq_khz = 0; > /* when 0 use maxInputPxlClkPLLFrequencyInKHz from firmwareInfo*/