From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 263F086337; Fri, 20 Dec 2024 07:16:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734678998; cv=none; b=JovYzThrStigIlK4AdATVQJU1kc2ItazROgHtJveHh7z8tRdr3kU4PB6zuto5idRokpQOYGHrViJ31R+8Z1NaiL3y4wLu+dHAAjjCUawaHlmDO+CRwc+RWH+Yaw050rYv8dk1+4leZu1LzX1M4ON80Ot4wYO7mFaZysuQJGcBvE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734678998; c=relaxed/simple; bh=AVpIzouLcbndFNKIcBiRnthvIDG00QqQ6SA4H/OWDyQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Rm40SHvmrwmplmyoEs4+qrleuN87+8spjY/q4/t/zelI4V0y1xLTnorq8TrYrJgkJOM6fHYmrBmQaRtoWfSuGlVNY2S6jb2JPOAqV49zQIDt9JjEJITfMQlEBmoGCnb/tT/V2RWwAFEdoltoL9mDXit7CSWOQ6Odw0fDAgoGTF4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=sQzJdpiL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="sQzJdpiL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CA33DC4CECD; Fri, 20 Dec 2024 07:16:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1734678997; bh=AVpIzouLcbndFNKIcBiRnthvIDG00QqQ6SA4H/OWDyQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=sQzJdpiLg87kcixCyS+nAPMIgEZvGXAUDSaAAyyrazwVDCnK6PVUMphaUXYaolk2S 5bfnudmHmClXlCpchsViHbCmKWBrsAPPT1QlOZxJ9YIv0Y5Y2hyz+7zFBF6NAB52xv LaNzifGz2SuddA6Q8gChTa2/wxwuzRxPUVXs6KSw7o939vHKSSYZ3rE+xWmvChG8IQ H/OUl3W8FJWJ76ne17WQoBC3y5tsXp7sR9KqpYaZvOE21kEgzfjKZqiMp++Szuks18 hRs/9FDv6MdKn0jL5dkg5fLKikfqQKPz3RcHuz3HZN24JcyIK0kfEM/jOI7ZWeliSV uDsRj/FkHLS9A== Message-ID: <99b481f1-7e0d-4c78-8099-6a6466f6a87a@kernel.org> Date: Fri, 20 Dec 2024 08:16:34 +0100 Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] tty: mips_ejtag_fdc: Call cpu_relax() in registers polling busy loops To: Zhongqiu Han , gregkh@linuxfoundation.org Cc: linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org References: <20241219124254.321778-1-quic_zhonhan@quicinc.com> Content-Language: en-US From: Jiri Slaby Autocrypt: addr=jirislaby@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 19. 12. 24, 13:42, Zhongqiu Han wrote: > It is considered good practice to call cpu_relax() in busy loops, see > Documentation/process/volatile-considered-harmful.rst. This can lower CPU > power consumption or yield to a hyperthreaded twin processor, or serve as > a compiler barrier. In addition, if something goes wrong in the busy loop > at least it can prevent things from getting worse. > > Signed-off-by: Zhongqiu Han > --- > drivers/tty/mips_ejtag_fdc.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/tty/mips_ejtag_fdc.c b/drivers/tty/mips_ejtag_fdc.c > index afbf7738c7c4..b17ead1e9698 100644 > --- a/drivers/tty/mips_ejtag_fdc.c > +++ b/drivers/tty/mips_ejtag_fdc.c > @@ -346,7 +346,7 @@ static void mips_ejtag_fdc_console_write(struct console *c, const char *s, > > /* Busy wait until there's space in fifo */ > while (__raw_readl(regs + REG_FDSTAT) & REG_FDSTAT_TXF) > - ; > + cpu_relax(); > __raw_writel(word.word, regs + REG_FDTX(c->index)); > } > out: > @@ -1233,7 +1233,7 @@ static void kgdbfdc_push_one(void) > > /* Busy wait until there's space in fifo */ > while (__raw_readl(regs + REG_FDSTAT) & REG_FDSTAT_TXF) > - ; > + cpu_relax(); Can this instead be switched to read_poll_timeout_atomic() or alike? Those already contain cpu_relax(), of course... thanks, -- js suse labs