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Subject: Re: Regression in 5.4 kernel on 32-bit Radeon IBM T40
To:     Woody Suwalski <terraluna977@gmail.com>
Cc:     =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        "Deucher, Alexander" <alexander.deucher@amd.com>,
        linux-kernel@vger.kernel.org, Pavel Machek <pavel@ucw.cz>
References: <400f6ce9-e360-0860-ca2a-fb8bccdcdc9b@gmail.com>
From:   Meelis Roos <mroos@linux.ee>
Message-ID: <1e6a6ccb-a7a0-4173-d667-a53eb99b8699@linux.ee>
Date:   Sun, 15 Dec 2019 18:04:09 +0200
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15.12.19 05:17 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.

I have the same problem on 32-bit Dell Latitude D600.

> 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.

Tried this on top on 5.4.0 and it helped here too.

-- 
Meelis Roos <mroos@linux.ee>