Messages in this thread | | | Date | Thu, 9 Jan 2020 15:14:36 +0100 | From | Christoph Hellwig <> | Subject | Re: Regression in 5.4 kernel on 32-bit Radeon IBM T40 |
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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?
> 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.
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