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Message-ID: <aa80728e-a2fc-4b2a-b441-fc884abd0535@broadcom.com>
Date: Fri, 3 May 2024 13:08:56 -0700
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Subject: Re: [PATCH 6/6] bmips: dma: drop redundant boot_cpu_type in
 arch_dma_sync
To: Christian Marangi <ansuelsmth@gmail.com>
Cc: Hauke Mehrtens <hauke@hauke-m.de>, =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?=
 <zajec5@gmail.com>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
 Rob Herring <robh@kernel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
 Conor Dooley <conor+dt@kernel.org>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@broadcom.com>,
 =?UTF-8?Q?=C3=81lvaro_Fern=C3=A1ndez_Rojas?= <noltari@gmail.com>,
 linux-mips@vger.kernel.org, devicetree@vger.kernel.org,
 linux-kernel@vger.kernel.org, =?UTF-8?Q?Daniel_Gonz=C3=A1lez_Cabanelas?=
 <dgcbueu@gmail.com>
References: <20240503135455.966-1-ansuelsmth@gmail.com>
 <20240503135455.966-7-ansuelsmth@gmail.com>
 <4821338d-bae1-418e-b4a8-6218f62d74dd@broadcom.com>
 <66353d60.050a0220.df862.761f@mx.google.com>
From: Florian Fainelli <florian.fainelli@broadcom.com>
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In-Reply-To: <66353d60.050a0220.df862.761f@mx.google.com>
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On 5/3/24 12:39, Christian Marangi wrote:
> On Fri, May 03, 2024 at 12:07:45PM -0700, Florian Fainelli wrote:
>> On 5/3/24 06:54, Christian Marangi wrote:
>>> Drop redundant boot_cpu_type in arch_sync_dma_for_cpu_all. These needs
>>> to be parsed only once and we can make use of bmips_rac_flush_disable to
>>> disable RAC flush on unsupported CPU.
>>>
>>> Set this value in bmips_cpu_setup for unsupported CPU to skip this
>>> redundant check every time DMA needs to be synced.
>>>
>>> Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
>>
>> You are taking a shortcut that is reasonable in premise, but keying off the
>> bmips_rac_flush_disable is IMHO misleading. The RAC is enabled in the
>> BMIPS5000 and BMIPS5200 cores, just it does not need SW management unlike
>> earlier cores.
>>
>> If you renamed it to bmips_rac_flush_needed that might be more compelling.
>> Also, the other reason is that on a kernel that was configured for
>> supporting only BMIPS5000 and BMIPS5200 CPUs, I think we could get some
>> decent dead code elimination of the boot_cpu_type() check, which would not
>> be the case.
> 
> I was a bit confused by the last part, should I drop this or just rename
> the variable? Cause I think for kernel that support ONLY those CPU I
> guess the DMA function will be optimized anyway since the bool will
> always be false I guess?

I don't think it can be optimized, I would drop that patch. This is a 
hot-path and so any optimization is welcome.
-- 
Florian


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