Re: [PATCH 00/18] ARM: Add minimal Raspberry Pi 4 support

[Stefan Wahren <wahrenst@xxxxxxx>]

Hi Nicolas,

Am 23.07.19 um 19:33 schrieb Nicolas Saenz Julienne:
> On Tue, 2019-07-23 at 18:26 +0200, Stefan Wahren wrote:
>> Hi Nicolas,
>>
>> thanks for your work, but i'm a little bit sceptical about these
>> changes. So here some thoughts.
>>
>> Am 23.07.19 um 15:32 schrieb Nicolas Saenz Julienne:
>>> On Tue, 2019-07-23 at 11:34 +0200, Christoph Hellwig wrote:
>>>> On Mon, Jul 22, 2019 at 08:10:17PM +0200, Stefan Wahren wrote:
>>>>> i rebased this series also and got this only on the RPi 4.
>>>>>
>>>>> After reverting the following:
>>>>>
>>>>> 79a986721de dma-mapping: remove dma_max_pfn
>>>>> 7559d612dff0 mmc: core: let the dma map ops handle bouncing
>>>>>
>>>>> This crash disappear, but wifi seems to be still broken.
>>>>>
>>>>> Would be nice, if you can investigate further.
>>>> That means dma addressing on this system doesn't just work for some
>>>> memory, and the mmc bounce buffering was papering over that just for
>>>> mmc.  Do you have highmem on this system?
>>>>
>>>> You might want to try this series, which has been submitted upstream:
>>>>
>>>>
> http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/arm-swiotlb
>>> Hi Christoph,
>>> I tried your series on top of Stefan's, it has no effect. I guess it's no
>>> surprise as with mult_v7_defconfig, you get SWIOTLB=n & LPAE=n.
>>>
>>> FYI DMA addressing constraints for RPi4 are the following: devices can only
>>> access the first GB of ram even though the board might have up to 4GB of
>>> ram.
>>> The DMA addresses are aliased with a 0xc0000000 offset. So 0x00000000 phys
>>> is
>>> aliased to 0xc0000000 in DMA. This is the same as for an RFC you commented
>>> last
>>> week trying to fix similar issues for arm64.
>>>
>>> You state in "arm: use swiotlb for bounce buffer on LPAE configs" that "The
>>> DMA
>>> API requires that 32-bit DMA masks are always supported". If I understand it
>>> correctly this device breaks that assumption. Which implies we need a bounce
>>> buffer system in place for any straming DMA user.
>>>
>>> It seems we're unable to use dma-direct/swiotlb, so I enabled arm's
>>> dmabounce
>>> on all devices hooked into RPi's limited interconnect, which fixes this
>>> issue.
>> Does it fix the wifi issue too?
> Well it works as long as I revert this: 901bb98918 ("nl80211: require and
> validate vendor command policy"). Which has nothing to do with DMA anyways.
>
> Was this the issue you where seeing?
Yes. So it's a regression? I will try to test it with a RPi 3B+