From: "Koenig, Christian" <Christian.Koenig@amd.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: "Christoph Hellwig" <hch@infradead.org>,
"Alex Deucher" <alexdeucher@gmail.com>,
"Michel Dänzer" <michel@daenzer.net>,
"Maxime Ripard" <maxime.ripard@bootlin.com>,
"Will Deacon" <will.deacon@arm.com>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"amd-gfx list" <amd-gfx@lists.freedesktop.org>,
"David Airlie" <airlied@linux.ie>,
"Huang, Ray" <Ray.Huang@amd.com>,
dri-devel <dri-devel@lists.freedesktop.org>,
"Michael Ellerman" <mpe@ellerman.id.au>,
"Zhang, Jerry" <Jerry.Zhang@amd.com>,
"Deucher, Alexander" <Alexander.Deucher@amd.com>,
"Sean Paul" <sean@poorly.run>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH] drm: disable WC optimization for cache coherent devices on non-x86
Date: Thu, 24 Jan 2019 11:23:44 +0000 [thread overview]
Message-ID: <57590a48-4629-e2a1-8673-ce9eb2ec210b@amd.com> (raw)
In-Reply-To: <CAKv+Gu9umPEmB+wh54NOTYcQ14oxf7rwVAXgCqo7V2A+VwkqPA@mail.gmail.com>
Am 24.01.19 um 10:59 schrieb Ard Biesheuvel:
> [SNIP]
> This is *exactly* my point the whole time.
>
> The current code has
>
> static inline bool drm_arch_can_wc_memory(void)
> {
> #if defined(CONFIG_PPC) && !defined(CONFIG_NOT_COHERENT_CACHE)
> return false;
>
> which means the optimization is disabled *unless the system is
> non-cache coherent*
>
> So if you have reports that the optimization works on some PowerPC, it
> must be non-cache coherent PowerPC, because that is the only place
> where it is enabled in the first place.
>
>> The only problematic here actually seems to be ARM, so you should
>> probably just add an "#ifdef .._ARM return false;".
>>
> ARM/arm64 does not have a Kconfig symbol like
> CONFIG_NOT_COHERENT_CACHE, so we can only disable it everywhere. If
> there are non-coherent ARM systems that are currently working in the
> same way as those non-coherent PowerPC systems, we will break them by
> doing this.
Summing the things I've read so far for ARM up I actually think it
depends on a runtime configuration and not on compile time one.
So the whole idea of providing the device to the drm_*_can_wc_memory()
function isn't so far fetched.
But for now I do prefer working and slightly slower system over broken
one, so I think we should just disable this on ARM for now.
Christian.
next prev parent reply other threads:[~2019-01-24 11:24 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-21 10:06 [RFC PATCH] drm: disable WC optimization for cache coherent devices on non-x86 Ard Biesheuvel
2019-01-21 10:11 ` Koenig, Christian
2019-01-21 15:07 ` Christoph Hellwig
2019-01-21 15:33 ` Ard Biesheuvel
2019-01-21 15:59 ` Christoph Hellwig
2019-01-21 16:14 ` Ard Biesheuvel
2019-01-21 16:22 ` Christoph Hellwig
2019-01-21 16:30 ` Ard Biesheuvel
2019-01-21 16:35 ` Christoph Hellwig
2019-01-21 16:50 ` Ard Biesheuvel
2019-01-21 17:55 ` Michel Dänzer
2019-01-21 17:59 ` Ard Biesheuvel
2019-01-21 18:04 ` Michel Dänzer
2019-01-21 18:20 ` Ard Biesheuvel
2019-01-21 18:23 ` Michel Dänzer
2019-01-21 18:28 ` Ard Biesheuvel
2019-01-21 19:04 ` Michel Dänzer
2019-01-21 19:18 ` Ard Biesheuvel
2019-01-22 8:38 ` Ard Biesheuvel
2019-01-22 20:56 ` Alex Deucher
2019-01-22 21:07 ` Ard Biesheuvel
2019-01-23 7:15 ` Christoph Hellwig
2019-01-23 9:08 ` Ard Biesheuvel
2019-01-23 16:44 ` Christoph Hellwig
2019-01-23 16:52 ` Ard Biesheuvel
2019-01-24 9:13 ` Christoph Hellwig
2019-01-24 9:25 ` Koenig, Christian
2019-01-24 9:28 ` Ard Biesheuvel
2019-01-24 9:45 ` Koenig, Christian
2019-01-24 9:59 ` Ard Biesheuvel
2019-01-24 11:23 ` Koenig, Christian [this message]
2019-01-24 11:26 ` Ard Biesheuvel
2019-01-24 11:37 ` Koenig, Christian
2019-01-24 11:45 ` Ard Biesheuvel
2019-01-24 13:54 ` Alex Deucher
2019-01-24 13:57 ` Ard Biesheuvel
2019-01-24 14:00 ` Alex Deucher
2019-01-24 16:04 ` Michel Dänzer
2019-01-24 9:31 ` Michel Dänzer
2019-01-24 9:37 ` Ard Biesheuvel
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