Re: Regression in 5.4 kernel on 32-bit Radeon IBM T40

From: Meelis Roos
Date: Sun Dec 15 2019 - 11:04:49 EST

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@xxxxxx>
Date:ÂÂ Thu Aug 15 09:27:00 2019 +0200

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@xxxxxxxx>