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To: "'Dave Martin'" , "'Mark Rutland'" In-Reply-To: <20200608103340.GA31466@arm.com> Subject: RE: [PATCH] arm64: fpsimd: Added API to manage fpsimd state inside kernel Date: Thu, 11 Jun 2020 18:17:32 +0900 Message-ID: <000001d63fd1$23430d80$69c92880$@samsung.com> MIME-Version: 1.0 X-Mailer: Microsoft Outlook 16.0 Thread-Index: AQGxBksMB01Mym8I2jEMUBwtLj9rogIZEnF2AoMWIKECIyRV0KjmWITQ Content-Language: ko X-Brightmail-Tracker: H4sIAAAAAAAAA02TfUxTVxjGd3rv7YeOca0dnHW4NR3gZCu2zOKBAcEp5Oo2wub2B5uCFa6U rbRNC3MOMxFJ5UuYM8jkewHkwxJIqQgO3AZklbIQPgSDVCoDdCBfGxPCwnQtFxP+e855f895 3+ecHC7Gv8QRchPUSbROrVCJ2Vvw5s5dcolxeTxaOtgWgKoGijFUe/spjn6ctRJo4WoOQGkl bQDNGQowdK6igY3st6pZ6FHVOBt11Q+xkKE8Av2enYjsFgOBTBPDBBq8WcxGVXf7Wai1uJtA 49OjGPp+tpmFqq0tOLoyOgpQkykfQ+1PV3GUbpOjstFrLFR0u4IIFVLGUiOgilL7caohz45T prpMNjXf28uhfi4xcqimyjPUX7OTHGrh1hCbyjXXAWrJ9Frk1s9UQUpaEUfrRLQ6VhOXoI4P Fr9/OGZ/jNxfKpPIAtBesUitSKSDxQc+iJSEJ6gc+cWirxSqZMdWpEKvF+8OCdJpkpNokVKj TwoW09o4lVYm0/rqFYn6ZHW8b6wmMVAmlfrJHeQxlXLt8TBHm+369dhgJZEKzr+YBbhcSO6B S0+OZwEel0+2ANibGpYFtjj03w49e59gFssAXvhlEDgpp2Gh+TzOFNoBtJ6d3aCmAfyzoJHl pNikJ6yecRZ4XAH5Cezv+YfthDDyHgdOXOxeL/BICbzZs4g79XYHlDXZvt4CJ73gs+ryde1C BsC20kcEo7fB7iuT6zxGSuFCbxnG6NfhjblijBlPBFenrm40DocTNjNgGAEsyjRgziEgaeXB set9OGM4AO32HBajt8MZi5nDaCGczjNs6BRYXnGBw5gzAPwhs3PD8A40l1hZzE2+AbvubQz3 Eszo/I/DbLvADAOfoT3hiqmH/fz4BzMD2HdAXLgpWuGmaIWbohVuilAO8DrgRmv1ifG03k+7 Z/Nzm8D67/ChWkDR3KJvB2BxQQeAXEwscNnmPh7Nd4lTnPqG1mlidMkqWt8B5I7bvogJX47V OL6XOilGJvfz95cGyJHc3w+J3V3mA/ui+WS8Ion+kqa1tO65j8XlCVNZgaT6UOja0NS5a/yO hm/9a5pLO2uKQ+R+Oe+t3HCt7Vlmex+MsHi4vhXx2OfTULcCEiv3qCmaPj1vlobtndqff9n1 9O6jHn0nhPvGeltzG2wtbcgWlr92/aGNHzWCV8cuay+pDw6fufN50ODiq2/uILxfGL+fHtKU kiJ/uO+UVpTxsSDvROnJtJIjxIAyKqFl1yG2tRmWKt3XsIV3c6OaLk9GlaHDnuGNAtJraeYL w4rJ0ujq/ZGHba2fuPvHyOhOiWSHoOuVI5aTxvrs354cM0cQqgeyX2OI1X/f3pnOk1l6PlT+ NC1Mc6s/O1Ypq/EOGvE6unRcbzfX3nF7ZmzdOtUlxvVKhcwH0+kV/wMdzYR6pgQAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFvrLIsWRmVeSWpSXmKPExsWy7bCSnO6abw/jDE6ckrBYemkOs8XKE/9Y LBa+OcVq8X5ZD6NF09w9jBZv26YzWzQvXs9mcX/fciaL50sfslkcWXuVyaJtgZ/Fme5ci/vH 21gtNj2+xmpxedccNoul1y8yWeycc5LV4uHL28wWk95sY7JYfmoHi8XM27cZLTZvmspssfff TxaLljumFvNvr2aymH1iMauDlMeaeWsYPWY3XGTxWN9/n8Vj06pONo93586xe+yfu4bdY/OS eo+Pb56we7zfd5XNo2/LKkaPz5vkArijuGxSUnMyy1KL9O0SuDL+vL7GXtDNX3Hv8hLWBsZ2 ni5GTg4JAROJ99vaWboYuTiEBHYzSnRemMAKkZCSONSwkB3CFpa433IELC4k8JxRYsZ8aRCb TUBFYvmrN2BxEYEQiYUHL7GCDGIWeMcusbizhwli6i1GiVmXJ7GAVHEK6ErsOv0BzBYWCJLY cRBiKouAqsT/5QsYQWxeAUuJPfOes0LYghInZz4Bq2cWMJI4d2g/G4QtL7H97RxmiOsUJH4+ XQZ1hZvE4ztbGCFqRCRmd7YxT2AUnoVk1Cwko2YhGTULScsCRpZVjJKpBcW56bnFhgWGeanl esWJucWleel6yfm5mxjBKURLcwfj9lUf9A4xMnEwHmKU4GBWEuEVFH8YJ8SbklhZlVqUH19U mpNafIhRmoNFSZz3RuHCOCGB9MSS1OzU1ILUIpgsEwenVANTv8SK5N0mH9arrlXqef9WIL7s l2cn++5am2CnSZ/X2b/IWHTcT663zMbn75w3mycWpth1S/YUdhRY2R7ZHVGt9H2+yp8jSXqZ HWeDUj/dssnWCzn5v+vo5U8Pbm6ocPmfvd5729zz53fseSVtb/LgtJqIvHbm0b3ZW6ft3dYc 8dx43lSJlBOKdfphNf8FtDwPX90Z1cG/SPiV3bpFP14VWe6M2S5Zs0X9jM+XZcxCk4INP7vc Wv5CbVdCGZuD09o/Le2/1V/vPN7221r8Vfwawyuuf5oDdcMdN54xEElRbRbMmzc5bH/Hrfw+ 73suU7cfnjO7feeHvxuTzkT/MZiXl6i8jL3FoOfI57CGOms9JZbijERDLeai4kQA57+L8JAD AAA= X-CMS-MailID: 20200611091732epcas2p1679c29715275a95f62f01c0851764bd9 X-Msg-Generator: CA X-Sendblock-Type: AUTO_CONFIDENTIAL CMS-TYPE: 102P DLP-Filter: Pass X-CFilter-Loop: Reflected X-CMS-RootMailID: 20200605073214epcas2p1576f3f90dbcefaad6180f2559ca5980d References: <20200605073052.23044-1-wooy88.kim@samsung.com> <20200605103705.GD85498@C02TD0UTHF1T.local> <20200608103340.GA31466@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200611_021741_471168_0EF8FED4 X-CRM114-Status: GOOD ( 16.05 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: 'Catalin Marinas' , 'Bhupesh Sharma' , 'Julien Grall' , 'Vincenzo Frascino' , 'Will Deacon' , yhwan.joo@samsung.com, 'Anisse Astier' , 'Marc Zyngier' , 'Allison Randal' , 'Sanghoon Lee' , jihun.kim@samsung.com, 'Kees Cook' , 'Suzuki K Poulose' , 'Wooki Min' , 'Kristina Martsenko' , 'Jeongtae Park' , 'Thomas Gleixner' , linux-arm-kernel@lists.infradead.org, 'Steve Capper' , 'Greg Kroah-Hartman' , linux-kernel@vger.kernel.org, 'James Morse' , 'Sudeep Holla' , dh.han@samsung.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Dear Dave Martin & Mark Rutland Thank you for your kind answer. > On Fri, Jun 05, 2020 at 11:37:05AM +0100, Mark Rutland wrote: > > Hi Wooyeon, > > > > There are a *lot* of people Cc' here, many of whomo will find this > > irrelevant. Please try to keep the Cc list constrained to a reasonable > > number of interested parties. I have adjusted the mailing list according to your opinion. > > Please introduce the problem you are trying to solve in more detail. > > We already have kernel_neon_{begin,end}() for kernel-mode NEON; why is > > that not sufficient for your needs? Please answer this before > > considering other details. > > > > What do you want to use this for? > Ack, this looks supicious. Can you explain why your usecase _requires_ > FPSIMD in hardirq context? > > For now, these functions are strictly for EFI use only and should never be > used by modules. I am in charge of camera driver development in Samsung S.LSI division. In order to guarantee real time processing such as Camera 3A algorithm in current or ongoing projects, prebuilt binary is loaded and used in kernel space, rather than user space. Because the binary is built with other standard library which could use FPSIMD register, kernel API should keep the original FPSIMD state for other user tasks. It is mostly used for internal kernel operation including hardirq context. (ex> hardIRQ context, kernel API called by user, kernel task) In the case of the kernel_neon_begin / kernel_neon_end that you mentioned, there is a limitation that cannot be used in hardirq context. Also, if another kernel task switching occurs while kernel API is being used, fpsimd register corruption may occur. In addition to kernel_neon_* API, It was necessary to add and utilize API considering kernel context. It is for this reason that I have tried to utilize efi_fpsimd_begin/end. Regards Wooyeon Kim _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel