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Re: framebuffer corruption due to overlapping stp instructions on arm64

From: Pavel Machek <pavel at ucw dot cz>
To: Mikulas Patocka <mpatocka at redhat dot com>
Cc: Andrew Pinski <pinskia at gmail dot com>, Richard Earnshaw <Richard dot Earnshaw at arm dot com>, ard dot biesheuvel at linaro dot org, Ramana Radhakrishnan <ramana dot gcc at googlemail dot com>, Florian Weimer <fweimer at redhat dot com>, thomas dot petazzoni at free-electrons dot com, GNU C Library <libc-alpha at sourceware dot org>, Catalin Marinas <catalin dot marinas at arm dot com>, Will Deacon <will dot deacon at arm dot com>, linux at armlinux dot org dot uk, LKML <linux-kernel at vger dot kernel dot org>, linux-arm-kernel at lists dot infradead dot org
Date: Sun, 5 Aug 2018 23:51:50 +0200
Subject: Re: framebuffer corruption due to overlapping stp instructions on arm64
References: <alpine.LRH.2.02.1808021242320.31834@file01.intranet.prod.int.rdu2.redhat.com> <CA+=Sn1mWkjuwVnjw6OWWUM=UcP76bdFa680FebCseewHfx3NpA@mail.gmail.com> <9acdacdb-3bd5-b71a-3003-e48132ee1371@redhat.com> <CAJA7tRZbmnZq7RfvQeYEy_a1ZObWqpFpVdvgsXgsioQ3RyPMuA@mail.gmail.com> <CAKv+Gu97QvwoLLK_zueiA_gjg_4Q5cqU4YVUyHUVFFfffdyJaw@mail.gmail.com> <11f9185a-7f71-83df-3a57-0a0ae9c1f934@arm.com> <alpine.LRH.2.02.1808032046540.24748@file01.intranet.prod.int.rdu2.redhat.com> <CA+=Sn1=6F-fGLmXE0VqQHTqTCUKUT=Fz29mMT7349SPFisbZ9A@mail.gmail.com> <alpine.LRH.2.02.1808040611070.23762@file01.intranet.prod.int.rdu2.redhat.com>

Hi!

> > Can you run the test program on x86 using the similar framebuffer
> > setup?  Does doing two writes (one aligned and one unaligned but
> > overlapping with previous one) cause the same issue?  I suspect it
> > does, then using memcpy for frame buffers is wrong.

I'm pretty sure it will work ok on x86.

> Overlapping unaligned writes work on x86 - they have to, because of 
> backward compatibility.

It is not that easy. 8086s (and similar) did not have MTRRs and PATs
either. Overlapping unaligned writes _on main memory_, _with normal
MTRR settings_ certainly work ok on x86.

Chances is memory type can be configured to work similar way on your
ARM/PCIe case?

> 8086, 80286 and 80386 didn't have any cache at all.

386s had cache (but not on die).
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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Follow-Ups:
- Re: framebuffer corruption due to overlapping stp instructions on arm64
  - From: Mikulas Patocka

References:
- framebuffer corruption due to overlapping stp instructions on arm64
  - From: Mikulas Patocka
- Re: framebuffer corruption due to overlapping stp instructions on arm64
  - From: Andrew Pinski
- Re: framebuffer corruption due to overlapping stp instructions on arm64
  - From: Florian Weimer
- Re: framebuffer corruption due to overlapping stp instructions on arm64
  - From: Ramana Radhakrishnan
- Re: framebuffer corruption due to overlapping stp instructions on arm64
  - From: Ard Biesheuvel
- Re: framebuffer corruption due to overlapping stp instructions on arm64
  - From: Richard Earnshaw (lists)
- Re: framebuffer corruption due to overlapping stp instructions on arm64
  - From: Mikulas Patocka
- Re: framebuffer corruption due to overlapping stp instructions on arm64
  - From: Andrew Pinski
- Re: framebuffer corruption due to overlapping stp instructions on arm64
  - From: Mikulas Patocka

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