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Wed, 02 Oct 2024 05:41:24 -0700 (PDT) Received: from [192.168.2.177] ([207.188.162.240]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a93c27c7237sm858830866b.81.2024.10.02.05.41.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 02 Oct 2024 05:41:23 -0700 (PDT) Message-ID: <7d577541-cada-4f6f-8e83-c420dd0e9382@gmail.com> Date: Wed, 2 Oct 2024 14:41:22 +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> 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: 7bit 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(). 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;