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SubjectRe: use generic DMA mapping code in powerpc V4
Hi All,

We still have some issues with PCI cards in our FSL P5020 and P5040
systems since the DMA mapping updates. [1, 2]

We have to limit the RAM to 3500MB for some problematic PCI cards.
(kernel boot argument 'mem=3500M')

The problematic DMA mapping code was added with the PowerPC updates
4.21-1 to the official kernel source code last year. [3]

We have created a bug report. [4]

The old 4.x kernels aren't affected because they use the old DMA code.

Please check the new DMA code again.



On 28 November 2018 at 4:55 pm, Christian Zigotzky wrote:
> On 28 November 2018 at 12:05PM, Michael Ellerman wrote:
>> Nothing specific yet.
>> I'm a bit worried it might break one of the many old obscure platforms
>> we have that aren't well tested.
> Please don't apply the new DMA mapping code if you don't be sure if it
> works on all supported PowerPC machines. Is the new DMA mapping code
> really necessary? It's not really nice, to rewrote code if the old
> code works perfect. We must not forget, that we work for the end
> users. Does the end user have advantages with this new code? Is it
> faster? The old code works without any problems. I am also worried
> about this code. How can I test this new DMA mapping code?
> Thanks

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