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 CA0641CF5E7 for ; Wed, 2 Oct 2024 12:43:49 +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=1727873031; cv=none; b=mX9Ow5kgpYZSpGdUWJQvwG86gluRvldQ042CN5ZzqnW3K2ea0g6Y78EOikiQ7//gsrVjiEwaRwoo3Ux7T5AvBiYwZKYtAQFTa32NDhh/qs02F/Qw09NP00LH0vTT21A77HT2gX+9lhgXzUvQZmgP7sl44Ln3l0ZCkhBvhMcMMks= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727873031; c=relaxed/simple; bh=/5kOhcdwjXgx7vKMb12UWt95fAbSNOwU04jH9iiXY00=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SQ8RQARZSpnccMmymKJUElOGmboHVr/sYG7OeB2c3C5KC6FZUIh1G4dqo2Gq76j0y+dZBhXjfOeHoCu0eP+1lxIZICaG3YK1z/kwWFwCSAv0+XNuZglfOpPCaoBUEkFGbsDAwRG+qEYRfjHyt52S/6VxUbWJsrvOYPzpkuBF28w= 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=LLs6tvRE; 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="LLs6tvRE" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1727873027; bh=/5kOhcdwjXgx7vKMb12UWt95fAbSNOwU04jH9iiXY00=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=LLs6tvREnjPZUmY4s9S5+TjmWVGcB+sV4A3kvshCpOSo6ww0Jb+79vGJpT/nqYKXT iGXNifw+e0JA4jdyv3urmzVMNOGZTwvSYpCGvaYpJAi/UpyNvlqG13p+TvtxJeNoe7 vpuZ+5YddxtblUpxhyz1zVgdvgfzaqtI/7O8zqXPH13tWGOH17Ad8Q4U2r0Q74mUcB 4V97ANnt66LFL7BrE03aCG1hD6Q+u/DVJMZALipQoj0KqjRGSUF8scJ9j3oN6ZtKcW Qn6KKIOeTTm17zZML+IaUI1yKhEj8BTIoMuasLCFxoOt5E1RxSmk9ynn3mVxcI3MuQ OpLt+QgbJLyFg== 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) server-digest SHA256) (No client certificate requested) (Authenticated sender: kholk11) by bali.collaboradmins.com (Postfix) with ESMTPSA id A4A2917E35DB; Wed, 2 Oct 2024 14:43:47 +0200 (CEST) Message-ID: <06c5573b-8b63-4a75-8af2-d6aace86fe69@collabora.com> Date: Wed, 2 Oct 2024 14:43:47 +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> From: AngeloGioacchino Del Regno Content-Language: en-US In-Reply-To: <7d577541-cada-4f6f-8e83-c420dd0e9382@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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. Perhaps I can add a comment stating "this is very unlikely to happen and should be dropped after thorough cleanup", if that's better? 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; -- AngeloGioacchino Del Regno Senior Software Engineer Collabora Ltd. 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