linux-kernel - Re: [PATCH 6/6] bmips: dma: drop redundant boot_cpu_type in arch_dma

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Message-ID: <4821338d-bae1-418e-b4a8-6218f62d74dd@broadcom.com>
Date: Fri, 3 May 2024 12:07:45 -0700
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Christian Marangi <ansuelsmth@...il.com>,
 Hauke Mehrtens <hauke@...ke-m.de>, Rafał Miłecki
 <zajec5@...il.com>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
 Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>,
 Álvaro Fernández Rojas <noltari@...il.com>,
 linux-mips@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, Daniel González Cabanelas
 <dgcbueu@...il.com>
Subject: Re: [PATCH 6/6] bmips: dma: drop redundant boot_cpu_type in
 arch_dma_sync

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@...il.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.
-- 
Florian


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