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([2a01:e0a:3d9:2080::fa42:7768]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-432bd0e180csm42176801f8f.10.2026.01.13.01.48.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 Jan 2026 01:48:27 -0800 (PST) Message-ID: Date: Tue, 13 Jan 2026 10:48:26 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Neil Armstrong Subject: Re: [PATCH] needsreview! arm64: dts: qcom: sdm845: Add missing MDSS reset To: david@ixit.cz, Bjorn Andersson , Konrad Dybcio , Rob Herring , Krzysztof Kozlowski , Conor Dooley Cc: Petr Hodina , linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, phone-devel@vger.kernel.org References: <20260112-mdss-reset-v1-1-af7c572204d3@ixit.cz> From: Neil Armstrong Content-Language: en-US, fr Autocrypt: addr=neil.armstrong@linaro.org; keydata= xsBNBE1ZBs8BCAD78xVLsXPwV/2qQx2FaO/7mhWL0Qodw8UcQJnkrWmgTFRobtTWxuRx8WWP GTjuhvbleoQ5Cxjr+v+1ARGCH46MxFP5DwauzPekwJUD5QKZlaw/bURTLmS2id5wWi3lqVH4 BVF2WzvGyyeV1o4RTCYDnZ9VLLylJ9bneEaIs/7cjCEbipGGFlfIML3sfqnIvMAxIMZrvcl9 qPV2k+KQ7q+aXavU5W+yLNn7QtXUB530Zlk/d2ETgzQ5FLYYnUDAaRl+8JUTjc0CNOTpCeik 80TZcE6f8M76Xa6yU8VcNko94Ck7iB4vj70q76P/J7kt98hklrr85/3NU3oti3nrIHmHABEB AAHNKk5laWwgQXJtc3Ryb25nIDxuZWlsLmFybXN0cm9uZ0BsaW5hcm8ub3JnPsLAkQQTAQoA OwIbIwULCQgHAwUVCgkICwUWAgMBAAIeAQIXgBYhBInsPQWERiF0UPIoSBaat7Gkz/iuBQJk Q5wSAhkBAAoJEBaat7Gkz/iuyhMIANiD94qDtUTJRfEW6GwXmtKWwl/mvqQtaTtZID2dos04 YqBbshiJbejgVJjy+HODcNUIKBB3PSLaln4ltdsV73SBcwUNdzebfKspAQunCM22Mn6FBIxQ GizsMLcP/0FX4en9NaKGfK6ZdKK6kN1GR9YffMJd2P08EO8mHowmSRe/ExAODhAs9W7XXExw UNCY4pVJyRPpEhv373vvff60bHxc1k/FF9WaPscMt7hlkbFLUs85kHtQAmr8pV5Hy9ezsSRa GzJmiVclkPc2BY592IGBXRDQ38urXeM4nfhhvqA50b/nAEXc6FzqgXqDkEIwR66/Gbp0t3+r yQzpKRyQif3OwE0ETVkGzwEIALyKDN/OGURaHBVzwjgYq+ZtifvekdrSNl8TIDH8g1xicBYp QTbPn6bbSZbdvfeQPNCcD4/EhXZuhQXMcoJsQQQnO4vwVULmPGgtGf8PVc7dxKOeta+qUh6+ SRh3vIcAUFHDT3f/Zdspz+e2E0hPV2hiSvICLk11qO6cyJE13zeNFoeY3ggrKY+IzbFomIZY 4yG6xI99NIPEVE9lNBXBKIlewIyVlkOaYvJWSV+p5gdJXOvScNN1epm5YHmf9aE2ZjnqZGoM Mtsyw18YoX9BqMFInxqYQQ3j/HpVgTSvmo5ea5qQDDUaCsaTf8UeDcwYOtgI8iL4oHcsGtUX oUk33HEAEQEAAcLAXwQYAQIACQUCTVkGzwIbDAAKCRAWmrexpM/4rrXiB/sGbkQ6itMrAIfn M7IbRuiSZS1unlySUVYu3SD6YBYnNi3G5EpbwfBNuT3H8//rVvtOFK4OD8cRYkxXRQmTvqa3 3eDIHu/zr1HMKErm+2SD6PO9umRef8V82o2oaCLvf4WeIssFjwB0b6a12opuRP7yo3E3gTCS KmbUuLv1CtxKQF+fUV1cVaTPMyT25Od+RC1K+iOR0F54oUJvJeq7fUzbn/KdlhA8XPGzwGRy 4zcsPWvwnXgfe5tk680fEKZVwOZKIEuJC3v+/yZpQzDvGYJvbyix0lHnrCzq43WefRHI5XTT QbM0WUIBIcGmq38+OgUsMYu4NzLu7uZFAcmp6h8g Organization: Linaro In-Reply-To: <20260112-mdss-reset-v1-1-af7c572204d3@ixit.cz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/12/26 13:33, David Heidelberg via B4 Relay wrote: > From: David Heidelberg > > If the OS does not support recovering the state left by the > bootloader it needs a way to reset display hardware, so that it can > start from a clean state. Add a reference to the relevant reset. > > Signed-off-by: David Heidelberg > --- > It efficiently fixes nothing for us (at least what we're aware), so I > assume the state left by bootloader is good enough In fact it does even more, perhaps in your usecase you're not affected but it permits resetting the MDSS while switching the IOMMU from bypass to translated. In the current IOMMU implementation, there's no current way to keep the IOMMU setup for an SID without a cut, leading to fatal IOMMU errors. With the hypervisor enabled, some IOMMU entries are left to fallback in bypass when switching, but in EL2 there's no fallback and the ARM SMMUv2 doesn't support mapping _before_ attaching to a device leading to: https://elixir.bootlin.com/linux/v6.18.4/source/drivers/iommu/iommu.c#L3046 /* * Drivers are supposed to allow mappings to be installed in a domain * before device attachment, but some don't. Hack around this defect by * trying again after attaching. If this happens it means the device * will not continuously have the IOMMU_RESV_DIRECT map. */ Sorry for the digression! Neil > > I sending this as a something "which seems right" and works for us in > sdm845-next tree. > > David > --- > arch/arm64/boot/dts/qcom/sdm845.dtsi | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/arm64/boot/dts/qcom/sdm845.dtsi b/arch/arm64/boot/dts/qcom/sdm845.dtsi > index bf2f9c04adba7..75c192eddc57c 100644 > --- a/arch/arm64/boot/dts/qcom/sdm845.dtsi > +++ b/arch/arm64/boot/dts/qcom/sdm845.dtsi > @@ -4550,6 +4550,7 @@ mdss: display-subsystem@ae00000 { > reg-names = "mdss"; > > power-domains = <&dispcc MDSS_GDSC>; > + resets = <&dispcc DISP_CC_MDSS_RSCC_BCR>; > > clocks = <&dispcc DISP_CC_MDSS_AHB_CLK>, > <&dispcc DISP_CC_MDSS_MDP_CLK>; > > --- > base-commit: f417b7ffcbef7d76b0d8860518f50dae0e7e5eda > change-id: 20260112-mdss-reset-06988f05af96 > > Best regards,