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([2a01:e0a:982:cbb0:5e59:c27b:747a:3f52]) by smtp.gmail.com with ESMTPSA id l11-20020adff48b000000b0031c3ee933b5sm10323520wro.108.2023.08.28.05.02.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 28 Aug 2023 05:02:01 -0700 (PDT) Message-ID: Date: Mon, 28 Aug 2023 14:02:00 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Neil Armstrong Reply-To: neil.armstrong@linaro.org Subject: Re: [PATCH 1/2] irqchip/qcom-pdc: don't read version register if it is not available Content-Language: en-US, fr To: Dmitry Baryshkov , Marc Zyngier Cc: "Maulik Shah (mkshah)" , Andy Gross , Bjorn Andersson , Konrad Dybcio , Thomas Gleixner , linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20230825213552.1646321-1-dmitry.baryshkov@linaro.org> <09d89b1c-8c78-7671-a385-99c6a8910fde@quicinc.com> <865y4zfppf.wl-maz@kernel.org> 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 Developer Services In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/08/2023 12:18, Dmitry Baryshkov wrote: > On Mon, 28 Aug 2023 at 13:04, Marc Zyngier wrote: >> >> On Mon, 28 Aug 2023 10:46:10 +0100, >> Dmitry Baryshkov wrote: >>> >>> On Mon, 28 Aug 2023 at 12:36, Maulik Shah (mkshah) >>> wrote: >>>> >>>> Hi Dmitry, >>>> >>>> This patch may be useful if there was a case where some PDCs don't have >>>> version register populated/available, >>>> In all PDC versions, version register is always available but due to reg >>>> size not good enough in device tree for SM8150 it failed to read. >>>> >>>> reg size in device node must be expanded if its too small to access all >>>> registers and i think >>>> additional check in driver to check if size is good enough would not be >>>> of much use. >>> >>> Unfortunately, it doesn't work this way. DT files are ABI. Even if we >>> change the DT, the kernel should continue working with the older >>> version. >>> Thus, we have to add such bandaid code, which will keep the kernel >>> from crashing if old DT was used. >> >> You're missing the point: all existing PDC HW have version register. >> The fact that the DT is crap doesn't invalidate this simple fact. It >> is thus perfectly possible for the driver to *ignore* the crap and do >> the right thing by expanding the size of the mapping, rather than >> falling back to the non-versioned code. > > Ah. Interesting idea. If that's the overall consensus I can send v2 > doing this. Not sure what is better though. Please take my PDC 3.2 patch in the same set! Neil > >> >> There is definitely precedents for this sort of behaviour, such as the >> ARM GICv2 probe code. >