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SubjectRe: Regression in 5.4 kernel on 32-bit Radeon IBM T40
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 <>
> 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 <>

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