From: "Christian König" <christian.koenig@amd.com>
To: Christoph Hellwig <hch@lst.de>, Woody Suwalski <terraluna977@gmail.com>
Cc: DRI mailing list <dri-devel@lists.freedesktop.org>,
LKML <linux-kernel@vger.kernel.org>,
"Deucher, Alexander" <alexander.deucher@amd.com>,
Pavel Machek <pavel@ucw.cz>
Subject: Re: Regression in 5.4 kernel on 32-bit Radeon IBM T40
Date: Thu, 9 Jan 2020 16:12:26 +0100 [thread overview]
Message-ID: <9ad75215-3ff1-ee76-9985-12fd78d6aa5f@amd.com> (raw)
In-Reply-To: <20200109141436.GA22111@lst.de>
Hi Christoph,
Am 09.01.20 um 15:14 schrieb Christoph Hellwig:
> Hi Woody,
>
> sorry for the late reply, I've been off to a vacation over the holidays.
>
> On Sat, Dec 14, 2019 at 10:17:15PM -0500, Woody Suwalski wrote:
>> Regression in 5.4 kernel on 32-bit Radeon IBM T40
>> triggered by
>> commit 33b3ad3788aba846fc8b9a065fe2685a0b64f713
>> Author: Christoph Hellwig <hch@lst.de>
>> Date: Thu Aug 15 09:27:00 2019 +0200
>>
>> Howdy,
>> The above patch has triggered a display problem on IBM Thinkpad T40, where
>> the screen is covered with a lots of random short black horizontal lines,
>> or distorted letters in X terms.
>>
>> The culprit seems to be that the dma_get_required_mask() is returning a
>> value 0x3fffffff
>> which is smaller than dma_get_mask()0xffffffff.That results in
>> dma_addressing_limited()==0 in ttm_bo_device(), and using 40-bits dma
>> instead of 32-bits.
> Which is the intended behavior assuming your system has 1GB of memory.
> Does it?
Assuming the system doesn't have the 1GB split up somehow crazy over the
address space that should indeed work as intended.
>
>> If I hardcode "1" as the last parameter to ttm_bo_device_init() in place of
>> a call to dma_addressing_limited(),the problem goes away.
> I'll need some help from the drm / radeon / TTM maintainers if there are
> any other side effects from not passing the need_dma32 paramters.
> Obviously if the device doesn't have more than 32-bits worth of dram and
> no DMA offset we can't feed unaddressable memory to the device.
> Unfortunately I have a very hard time following the implementation of
> the TTM pool if it does anything else in this case.
The only other thing which comes to mind is using huge pages. Can you
try a kernel with CONFIG_TRANSPARENT_HUGEPAGE disabled?
Thanks,
Christian.
next prev parent reply other threads:[~2020-01-09 15:12 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-15 3:17 Regression in 5.4 kernel on 32-bit Radeon IBM T40 Woody Suwalski
2019-12-15 16:04 ` Meelis Roos
2020-01-09 14:14 ` Christoph Hellwig
2020-01-09 15:12 ` Christian König [this message]
2020-01-09 22:40 ` Woody Suwalski
2020-01-10 2:40 ` Woody Suwalski
2020-03-14 22:06 ` Thomas Schwinge
2020-02-22 16:16 ` Thomas Backlund
2020-09-16 22:15 ` Alex Deucher
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