[PATCH] drm/radeon: insist on 32-bit DMA for Cedar on PPC64/PPC64LE

[Christian König]

Hi Ben,

> I mentioned the HD 5450 purely as a matter of archeological interest.
Ok, in that case looking at the lspci -tv output doesn't tell us 
anything new.

> I suspected, but couldn't prove, that the problem might have something
> to do with the bridge (IBM POWER8 Host Bridge (PHB3)).

In that case you would see the problem with the caicos as well.

Or are there issues random enough that there could actually be some 
problem with the caicos as well and we haven't noticed it so far?

See it is really really odd that this should only happen with the cedar. 
On the other hand if it works for now, I don't see much issue having 
this workaround.

Regards,
Christian.

Am 23.02.2018 um 17:02 schrieb Ben Crocker:
> Hi Christian, Michel, Alex, et al.,
>
> I mentioned the HD 5450 purely as a matter of archeological interest.
>
> Back to the FirePro 2270 and Embedded Radeon E6465:
>
> I've attached text from both "lspci -tv" and "lspci -v."
> Actually I'm attaching a couple of different "lspci -v" outputs, one
> with the FirePro 2270 in place and one with the E6465 in (the same) place.
>
> I suspected, but couldn't prove, that the problem might have something
> to do with the bridge (IBM POWER8 Host Bridge (PHB3)).
>
> But I want to reiterate:
>
>   * Cedar GPU -> problem (before patch, that is);
>   * Caicos GPU in the same slot -> no problem
>
>
> -- Ben
>
> P.S.  Alex, thanks for applying the patch so expeditiously!
>
>
> On Fri, Feb 23, 2018 at 2:45 AM, Christian König 
> <ckoenig.leichtzumerken at gmail.com 
> <mailto:ckoenig.leichtzumerken at gmail.com>> wrote:
>
>     Am 22.02.2018 um 18:56 schrieb Michel Dänzer:
>
>         On 2018-02-22 06:37 PM, Ben Crocker wrote:
>
>             One of my colleagues did discover a "Radeon HG 5450 PCI"
>             from February
>             2010 which did, apparently, have a Cedar GPU and very
>             definitely had a
>             (plain old) PCI connector.
>
>         There must be a PCIe-to-PCI bridge on that board. The GPU
>         itself is
>         always PCIe, and treated accordingly by the driver.
>
>
>     Ben, just an educated guess but is this one the one which is
>     failing to work correctly?
>
>     Cause the PCIe bus interface is pretty much identical over all
>     generations of the last decade or so. Only the newest Vega10
>     generation is a bit different.
>
>     So I strongly thing that this isn't related to the device being a
>     Cedar at all, but rather that you have a bridge above it which
>     doesn't correctly handle 64bit transfers.
>
>     Can you please send and "lspci -t" of both the working and the
>     problematic devices?
>
>     Thanks,
>     Christian.
>
>

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