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[85.29.92.32]) by smtp.gmail.com with ESMTPSA id v7-20020ac25587000000b004fe3229e584sm768475lfg.270.2023.08.11.09.23.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Aug 2023 09:23:40 -0700 (PDT) Message-ID: <37cf3e0d-5a30-466f-86d3-cda077c3921f@gmail.com> Date: Fri, 11 Aug 2023 19:25:42 +0300 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 03/11] drm/bridge: tc358768: Cleanup PLL calculations Content-Language: en-US To: Tomi Valkeinen , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , David Airlie , Daniel Vetter , Francesco Dolcini Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Aradhya Bhatia References: <20230804-tc358768-v1-0-1afd44b7826b@ideasonboard.com> <20230804-tc358768-v1-3-1afd44b7826b@ideasonboard.com> From: =?UTF-8?Q?P=C3=A9ter_Ujfalusi?= In-Reply-To: <20230804-tc358768-v1-3-1afd44b7826b@ideasonboard.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/08/2023 13:44, Tomi Valkeinen wrote: > As is quite common, some of TC358768's PLL register fields are to be > programmed with (value - 1). Specifically, the FBD and PRD, multiplier > and divider, are such fields. > > However, what the driver currently does is that it considers that the > formula used for PLL rate calculation is: > > RefClk * [(FBD + 1)/ (PRD + 1)] * [1 / (2^FRS)] > > where FBD and PRD are values directly from the registers, while a more > sensible way to look at it is: > > RefClk * FBD / PRD * (1 / (2^FRS)) > > and when the FBD and PRD values are written to the registers, they will > be subtracted by one. > > Change the driver accordingly, as it simplifies the PLL code. Reviewed-by: Peter Ujfalusi > > Signed-off-by: Tomi Valkeinen > --- > drivers/gpu/drm/bridge/tc358768.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c > index b668f77673c3..d5831a1236e9 100644 > --- a/drivers/gpu/drm/bridge/tc358768.c > +++ b/drivers/gpu/drm/bridge/tc358768.c > @@ -316,7 +316,7 @@ static int tc358768_calc_pll(struct tc358768_priv *priv, > > target_pll = tc358768_pclk_to_pll(priv, mode->clock * 1000); > > - /* pll_clk = RefClk * [(FBD + 1)/ (PRD + 1)] * [1 / (2^FRS)] */ > + /* pll_clk = RefClk * FBD / PRD * (1 / (2^FRS)) */ > > for (i = 0; i < ARRAY_SIZE(frs_limits); i++) > if (target_pll >= frs_limits[i]) > @@ -336,19 +336,19 @@ static int tc358768_calc_pll(struct tc358768_priv *priv, > best_prd = 0; > best_fbd = 0; > > - for (prd = 0; prd < 16; ++prd) { > - u32 divisor = (prd + 1) * (1 << frs); > + for (prd = 1; prd <= 16; ++prd) { > + u32 divisor = prd * (1 << frs); > u32 fbd; > > - for (fbd = 0; fbd < 512; ++fbd) { > + for (fbd = 1; fbd <= 512; ++fbd) { > u32 pll, diff, pll_in; > > - pll = (u32)div_u64((u64)refclk * (fbd + 1), divisor); > + pll = (u32)div_u64((u64)refclk * fbd, divisor); > > if (pll >= max_pll || pll < min_pll) > continue; > > - pll_in = (u32)div_u64((u64)refclk, prd + 1); > + pll_in = (u32)div_u64((u64)refclk, prd); > if (pll_in < 4000000) > continue; > > @@ -611,7 +611,7 @@ static int tc358768_setup_pll(struct tc358768_priv *priv, > mode->clock * 1000); > > /* PRD[15:12] FBD[8:0] */ > - tc358768_write(priv, TC358768_PLLCTL0, (prd << 12) | fbd); > + tc358768_write(priv, TC358768_PLLCTL0, ((prd - 1) << 12) | (fbd - 1)); > > /* FRS[11:10] LBWS[9:8] CKEN[4] RESETB[1] EN[0] */ > tc358768_write(priv, TC358768_PLLCTL1, > -- Péter