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[176.184.41.228]) by smtp.gmail.com with ESMTPSA id l4-20020a7bc444000000b003f4272c2d0csm2875134wmi.36.2023.05.19.09.43.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 19 May 2023 09:43:30 -0700 (PDT) Message-ID: <1eb91ba2-a2e0-44e4-a07b-badccef1fe42@linaro.org> Date: Fri, 19 May 2023 18:43:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH v6 1/4] bswap: Add the ability to store to an unaligned 24 bit field Content-Language: en-US To: Jonathan Cameron Cc: qemu-devel@nongnu.org, Michael Tsirkin , Fan Ni , linux-cxl@vger.kernel.org, linuxarm@huawei.com, Ira Weiny , Michael Roth , Dave Jiang , Markus Armbruster , =?UTF-8?Q?Daniel_P_=2e_Berrang=c3=a9?= , Eric Blake , Mike Maslenkin , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Thomas Huth References: <20230519141803.29713-1-Jonathan.Cameron@huawei.com> <20230519141803.29713-2-Jonathan.Cameron@huawei.com> <27f9ad4f-bdde-f548-860b-34e52493faa2@linaro.org> <20230519172404.0000649e@Huawei.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= In-Reply-To: <20230519172404.0000649e@Huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-cxl@vger.kernel.org On 19/5/23 18:24, Jonathan Cameron wrote: > On Fri, 19 May 2023 18:08:30 +0200 > Philippe Mathieu-Daudé wrote: > >> On 19/5/23 16:18, Jonathan Cameron wrote: >>> From: Ira Weiny >>> >>> CXL has 24 bit unaligned fields which need to be stored to. CXL is >>> specified as little endian. >>> >>> Define st24_le_p() and the supporting functions to store such a field >>> from a 32 bit host native value. >>> >>> The use of b, w, l, q as the size specifier is limiting. So "24" was >>> used for the size part of the function name. >>> >>> Signed-off-by: Ira Weiny >>> Signed-off-by: Jonathan Cameron >>> --- >>> docs/devel/loads-stores.rst | 1 + >>> include/qemu/bswap.h | 27 +++++++++++++++++++++++++++ >>> 2 files changed, 28 insertions(+) >>> >>> diff --git a/docs/devel/loads-stores.rst b/docs/devel/loads-stores.rst >>> index d2cefc77a2..82a79e91d9 100644 >>> --- a/docs/devel/loads-stores.rst >>> +++ b/docs/devel/loads-stores.rst >>> @@ -36,6 +36,7 @@ store: ``st{size}_{endian}_p(ptr, val)`` >>> ``size`` >>> - ``b`` : 8 bits >>> - ``w`` : 16 bits >>> + - ``24`` : 24 bits >>> - ``l`` : 32 bits >>> - ``q`` : 64 bits >>> >>> diff --git a/include/qemu/bswap.h b/include/qemu/bswap.h >>> index 15a78c0db5..f546b1fc06 100644 >>> --- a/include/qemu/bswap.h >>> +++ b/include/qemu/bswap.h >>> @@ -8,11 +8,25 @@ >>> #undef bswap64 >>> #define bswap64(_x) __builtin_bswap64(_x) >>> >>> +static inline uint32_t bswap24(uint32_t x) >>> +{ >>> + assert((x & 0xff000000U) == 0); >> >> Asserting here is a bit violent. In particular because there is no >> contract description that x should be less than N bits for bswapN() >> in "qemu/bswap.h" API. >> >> But if you rather to assert ... > > > I'm fine either way. You asked for it when reviewing v4... > https://lore.kernel.org/all/28a9d97a-b252-a33f-1ac0-cd36264b29ab@linaro.org/ Never too late to improve oneself ;) One month later I'm afraid the assertion would fire too often, resulting in unnecessary pain to developers (in particular the non-QEMU ones). >> >>> + >>> + return (((x & 0x000000ffU) << 16) | >>> + ((x & 0x0000ff00U) << 0) | >>> + ((x & 0x00ff0000U) >> 16)); >>> +} >>> + >>> static inline void bswap16s(uint16_t *s) >>> { >>> *s = __builtin_bswap16(*s); >>> } >>> >>> +static inline void bswap24s(uint32_t *s) >>> +{ >>> + *s = bswap24(*s & 0x00ffffffU); >> >> ... and sanitize the value here ... >> >>> +} >>> + >>> static inline void bswap32s(uint32_t *s) >>> { >>> *s = __builtin_bswap32(*s); >>> @@ -26,11 +40,13 @@ static inline void bswap64s(uint64_t *s) >>> #if HOST_BIG_ENDIAN >>> #define be_bswap(v, size) (v) >>> #define le_bswap(v, size) glue(__builtin_bswap, size)(v) >>> +#define le_bswap24(v) bswap24(v) >> >> ... then shouldn't you sanitize also here? >> > > Good point. I forgot that detail whilst fighting with s390 > cross builds earlier ;) > >> Personally I'd just drop the assertion. > > I'm fine with doing that. > > Jonathan > >> >>> #define be_bswaps(v, size) >>> #define le_bswaps(p, size) \ >>> do { *p = glue(__builtin_bswap, size)(*p); } while (0) >>> #else >>> #define le_bswap(v, size) (v) >>> +#define le_bswap24(v) (v) >>> #define be_bswap(v, size) glue(__builtin_bswap, size)(v) >>> #define le_bswaps(v, size) >>> #define be_bswaps(p, size) \ >>> @@ -176,6 +192,7 @@ CPU_CONVERT(le, 64, uint64_t) >>> * size is: >>> * b: 8 bits >>> * w: 16 bits >>> + * 24: 24 bits >>> * l: 32 bits >>> * q: 64 bits >>> * >>> @@ -248,6 +265,11 @@ static inline void stw_he_p(void *ptr, uint16_t v) >>> __builtin_memcpy(ptr, &v, sizeof(v)); >>> } >>> >>> +static inline void st24_he_p(void *ptr, uint32_t v) >>> +{ >>> + __builtin_memcpy(ptr, &v, 3); >>> +} >>> + >>> static inline int ldl_he_p(const void *ptr) >>> { >>> int32_t r; >>> @@ -297,6 +319,11 @@ static inline void stw_le_p(void *ptr, uint16_t v) >>> stw_he_p(ptr, le_bswap(v, 16)); >>> } >>> >>> +static inline void st24_le_p(void *ptr, uint32_t v) >>> +{ >>> + st24_he_p(ptr, le_bswap24(v)); >>> +} >>> + >>> static inline void stl_le_p(void *ptr, uint32_t v) >>> { >>> stl_he_p(ptr, le_bswap(v, 32)); >> >> Conditional to removing the assertion in bswap24(): >> Reviewed-by: Philippe Mathieu-Daudé >> >