From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bali.collaboradmins.com (bali.collaboradmins.com [148.251.105.195]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9E6891D014A for ; Wed, 2 Oct 2024 13:02:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.251.105.195 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727874175; cv=none; b=S8bZF0428hf3WgzvPwG2m7Ahr8zHNGar2ndBxnvHJBJXC+83AYwUz6fsykbdr0F0xcpjzyQ42RsSRFHdbYBpdoCvKCvb2/4UJEIRnn0+gUU577Yl+CXpNwcG/WB35x1AXHnqheFkC7Ak+co874hMJMMOZ8KXGAlW4J72BoUk3jg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727874175; c=relaxed/simple; bh=/WVc7zeLQWX/DwF/gJgvocglZ0fzUFLwBuR134VmbqQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jwthFCBPa5clinIt0dSfIvrd0GcFtTxf9tH8Zk/oOmaweLbWqtspGyG3yNg0maA+793ww3NoBDhK0zArblMTeV7Imw4TOsvca3J6SEuOzlVGyWYwsmo004obRUVG/CvXaKDULPQSOvHf1uZ9nYl+t1eF/ZrxsElvfqhbPvo3XaM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b=jMQRTKSN; arc=none smtp.client-ip=148.251.105.195 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b="jMQRTKSN" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1727874171; bh=/WVc7zeLQWX/DwF/gJgvocglZ0fzUFLwBuR134VmbqQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=jMQRTKSNwaCjravGvUcTg4Fc2U2kpPYbw4JoigCrG5eB1wo3MNDp7HBMvS/4dnXEq RVjkimA4EjX+cSCPlujipioPxkkO+wjhYEvswxNy2Lu3VxUagXJ5rNrW/kAOYEl5Wq HcVbRZqGGJI2on88qzfoJ2LEnWTMySCv5SQy6nH0Kc3XCiNn6isKKvhhm0fwPuLlAf vbwlLKxKEvvTwQTewNO8JYCqPaiA/dcaqMzXG4dL2/g+7cMQPgkxqlJcprxczebh38 CHhSPJ4k7GbkMHqWhQaaLV+dq0jrIiyETTkJ7aG4w2+awRRxxsvDKDH6Cpzl6YTjkr E/BuKuEnnT/jA== Received: from [192.168.1.100] (2-237-20-237.ip236.fastwebnet.it [2.237.20.237]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) (Authenticated sender: kholk11) by bali.collaboradmins.com (Postfix) with ESMTPSA id AA5A417E35DE; Wed, 2 Oct 2024 15:02:51 +0200 (CEST) Message-ID: <5c5e3f7d-5ade-4625-bef9-4fcb7f717778@collabora.com> Date: Wed, 2 Oct 2024 15:02:51 +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: Matthias Brugger , 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> <2cb6e2d6-226f-4a40-bdff-81baff8988a6@gmail.com> From: AngeloGioacchino Del Regno Content-Language: en-US In-Reply-To: <2cb6e2d6-226f-4a40-bdff-81baff8988a6@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Il 02/10/24 14:58, Matthias Brugger ha scritto: > > > 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. > Let's drop it then. :-) >> 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)? > The reasoning behind all of this is that those functions are used in drivers' performance paths, including display and camera.... so a WARN_ON would be even more against what I'm trying to do. At this point we can just leave this as it is.... > 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; >>