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Wed, 02 Oct 2024 05:58:28 -0700 (PDT) Received: from [192.168.2.177] ([207.188.162.240]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a93c297c2d2sm859766966b.183.2024.10.02.05.58.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 02 Oct 2024 05:58:27 -0700 (PDT) Message-ID: <2cb6e2d6-226f-4a40-bdff-81baff8988a6@gmail.com> Date: Wed, 2 Oct 2024 14:58:26 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/3] soc: mediatek: mtk-cmdq: Mark very unlikely branches as such To: AngeloGioacchino Del Regno , linux-mediatek@lists.infradead.org Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kernel@collabora.com References: <20240918100620.103536-1-angelogioacchino.delregno@collabora.com> <20240918100620.103536-3-angelogioacchino.delregno@collabora.com> <7d577541-cada-4f6f-8e83-c420dd0e9382@gmail.com> <06c5573b-8b63-4a75-8af2-d6aace86fe69@collabora.com> Content-Language: en-US, ca-ES, es-ES From: Matthias Brugger Autocrypt: addr=matthias.bgg@gmail.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 02/10/2024 14:43, AngeloGioacchino Del Regno wrote: > Il 02/10/24 14:41, Matthias Brugger ha scritto: >> >> >> On 18/09/2024 12:06, AngeloGioacchino Del Regno wrote: >>> Calling cmdq packet builders with an unsupported event number, >>> or without left/right operands (in the case of logic commands) >>> means that the caller (another driver) wants to perform an >>> unsupported operation, so this means that the caller must be >>> fixed instead. >>> >>> Anyway, such checks are here for safety and, unless any driver >>> bug or any kind of misconfiguration is present, will always be >>> false so add a very unlikely hint for those. >>> >>> Knowing that CPUs' branch predictors (and compilers, anyway) are >>> indeed smart about these cases, this is done mainly for human >>> readability purposes. >>> >> >> Are you really sure we need that? As you mentioned the unlikely() is probably >> useless as compiler and branch predictions will do the job. I don't see the >> complexity in the code to have this annotations for human readability. >> >> I would argue against using unlikely() here as, in general, it is discouraged >> to use it. We will just create a data point of doing things that should only >> be done with very good reason. I don't see the reason here, it will only >> confuse other developers about the use of likely() and unlikely(). >> > > If you have strong opinions I have no problem dropping this. My take would be to drop it. > Perhaps I can add a comment stating "this is very unlikely to happen and should > be dropped after thorough cleanup", if that's better? > As these are exported functions they could be used by out-of-tree modules, so it could make sense to check the input parameter. Maybe transform it to WARN_ON(event >= CMDQ_MAX_EVENT)? Regards, Matthias > Cheers! > Angelo > >> Regards, >> Matthias >> >>> Signed-off-by: AngeloGioacchino Del Regno >>> >>> --- >>>   drivers/soc/mediatek/mtk-cmdq-helper.c | 10 +++++----- >>>   1 file changed, 5 insertions(+), 5 deletions(-) >>> >>> diff --git a/drivers/soc/mediatek/mtk-cmdq-helper.c >>> b/drivers/soc/mediatek/mtk-cmdq-helper.c >>> index 620c371fd1fc..4ffd1a35df87 100644 >>> --- a/drivers/soc/mediatek/mtk-cmdq-helper.c >>> +++ b/drivers/soc/mediatek/mtk-cmdq-helper.c >>> @@ -336,7 +336,7 @@ int cmdq_pkt_wfe(struct cmdq_pkt *pkt, u16 event, bool >>> clear) >>>       struct cmdq_instruction inst = { {0} }; >>>       u32 clear_option = clear ? CMDQ_WFE_UPDATE : 0; >>> -    if (event >= CMDQ_MAX_EVENT) >>> +    if (unlikely(event >= CMDQ_MAX_EVENT)) >>>           return -EINVAL; >>>       inst.op = CMDQ_CODE_WFE; >>> @@ -351,7 +351,7 @@ int cmdq_pkt_acquire_event(struct cmdq_pkt *pkt, u16 event) >>>   { >>>       struct cmdq_instruction inst = {}; >>> -    if (event >= CMDQ_MAX_EVENT) >>> +    if (unlikely(event >= CMDQ_MAX_EVENT)) >>>           return -EINVAL; >>>       inst.op = CMDQ_CODE_WFE; >>> @@ -366,7 +366,7 @@ int cmdq_pkt_clear_event(struct cmdq_pkt *pkt, u16 event) >>>   { >>>       struct cmdq_instruction inst = { {0} }; >>> -    if (event >= CMDQ_MAX_EVENT) >>> +    if (unlikely(event >= CMDQ_MAX_EVENT)) >>>           return -EINVAL; >>>       inst.op = CMDQ_CODE_WFE; >>> @@ -381,7 +381,7 @@ int cmdq_pkt_set_event(struct cmdq_pkt *pkt, u16 event) >>>   { >>>       struct cmdq_instruction inst = {}; >>> -    if (event >= CMDQ_MAX_EVENT) >>> +    if (unlikely(event >= CMDQ_MAX_EVENT)) >>>           return -EINVAL; >>>       inst.op = CMDQ_CODE_WFE; >>> @@ -476,7 +476,7 @@ int cmdq_pkt_logic_command(struct cmdq_pkt *pkt, u16 >>> result_reg_idx, >>>   { >>>       struct cmdq_instruction inst = { {0} }; >>> -    if (!left_operand || !right_operand || s_op >= CMDQ_LOGIC_MAX) >>> +    if (unlikely(!left_operand || !right_operand || s_op >= CMDQ_LOGIC_MAX)) >>>           return -EINVAL; >>>       inst.op = CMDQ_CODE_LOGIC; >