linux-kernel - Re: [PATCH v2] loongarch/mm: disable WUC for pgprot_writecombine as same as ioremap

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Message-ID: <80e0813a-0651-41cf-a82d-776acbf1a5bc@linux.dev>
Date: Thu, 19 Dec 2024 10:54:01 +0800
From: Sui Jingfeng <sui.jingfeng@...ux.dev>
To: Icenowy Zheng <uwu@...nowy.me>, Xi Ruoyao <xry111@...111.site>,
 WANG Xuerui <kernel@...0n.name>, Huacai Chen <chenhuacai@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 "Mike Rapoport (IBM)" <rppt@...nel.org>, Baoquan He <bhe@...hat.com>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 David Hildenbrand <david@...hat.com>, Zhen Lei <thunder.leizhen@...wei.com>,
 Thomas Gleixner <tglx@...utronix.de>, Zhihong Dong <donmor3000@...mail.com>,
 loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] loongarch/mm: disable WUC for pgprot_writecombine as
 same as ioremap_wc


On 2024/12/18 20:43, Icenowy Zheng wrote:
> For the fact of drm/ast's dramatical drop, it's because write to the
> framebuffer can no longer be reordered.


No, your understanding is wrong, very very wrong and a big wrong.

It's not because it can't reorder the write. Rather, it's because
that the CPU can't do write gathering and can't do burst write any
more.

So do you still think your patch is harmless?


-- 
Best regards,
Sui