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Fri, 13 Jun 2025 07:02:33 -0700 (PDT) Message-ID: Date: Fri, 13 Jun 2025 16:02:30 +0200 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 08/17] drm/msm/dsi/phy: Fix reading zero as PLL rates when unprepared To: Dmitry Baryshkov Cc: Abhinav Kumar , Sean Paul , Marijn Suijten , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Krishna Manikandan , Jonathan Marek , Kuogee Hsieh , Neil Armstrong , Dmitry Baryshkov , Bjorn Andersson , Michael Turquette , Stephen Boyd , Rob Clark , linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-clk@vger.kernel.org, Abel Vesa , Srinivas Kandagatla References: <20250610-b4-sm8750-display-v6-0-ee633e3ddbff@linaro.org> <20250610-b4-sm8750-display-v6-8-ee633e3ddbff@linaro.org> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzysztof.kozlowski@linaro.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 13/06/2025 15:55, Dmitry Baryshkov wrote: >> >> @@ -361,24 +373,47 @@ static int dsi_pll_7nm_lock_status(struct dsi_pll_7nm *pll) >> >> static void dsi_pll_disable_pll_bias(struct dsi_pll_7nm *pll) >> { >> + unsigned long flags; >> u32 data; >> >> + spin_lock_irqsave(&pll->pll_enable_lock, flags); >> + --pll->pll_enable_cnt; >> + if (pll->pll_enable_cnt < 0) { >> + spin_unlock_irqrestore(&pll->pll_enable_lock, flags); >> + DRM_DEV_ERROR_RATELIMITED(&pll->phy->pdev->dev, >> + "bug: imbalance in disabling PLL bias\n"); >> + return; >> + } else if (pll->pll_enable_cnt > 0) { >> + spin_unlock_irqrestore(&pll->pll_enable_lock, flags); >> + return; >> + } /* else: == 0 */ >> + >> data = readl(pll->phy->base + REG_DSI_7nm_PHY_CMN_CTRL_0); >> data &= ~DSI_7nm_PHY_CMN_CTRL_0_PLL_SHUTDOWNB; >> writel(0, pll->phy->pll_base + REG_DSI_7nm_PHY_PLL_SYSTEM_MUXES); >> writel(data, pll->phy->base + REG_DSI_7nm_PHY_CMN_CTRL_0); >> + spin_unlock_irqrestore(&pll->pll_enable_lock, flags); >> ndelay(250); > > What is this ndelay protecting? Is is to let the hardware to wind down > correctly? I'm worried about dsi_pll_disable_pll_bias() beng followed up > by dsi_pll_enable_pll_bias() in another thread, which would mean that > corresponding writes to the REG_DSI_7nm_PHY_CMN_CTRL_0 can come up > without any delay between them. > Great question, but why do you ask me? The code was there already and MSM DRM drivers are not something I know and could provide context about. Best regards, Krzysztof