linux-kernel - build failure from drm/ttm commit now in mainline (was: linux-next: build failure after merge of the drm tree)

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Date:   Wed, 26 Apr 2023 07:59:23 +0200
From:   Thorsten Leemhuis <regressions@...mhuis.info>
To:     Dave Airlie <airlied@...hat.com>,
        DRI <dri-devel@...ts.freedesktop.org>
Cc:     Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>,
        Christian König <christian.koenig@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux kernel regressions list <regressions@...ts.linux.dev>,
        Justin Forbes <jforbes@...hat.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: build failure from drm/ttm commit now in mainline (was: linux-next:
 build failure after merge of the drm tree)

Lo!

Sometimes the regression tracker runs into regressions himself... :-D

On 11.04.23 08:47, Stephen Rothwell wrote:
> 
> After merging the drm tree, today's linux-next build (powerpc
> allyesconfig) failed like this:
> 
> drivers/gpu/drm/ttm/ttm_pool.c:73:29: error: variably modified 'global_write_combined' at file scope
>    73 | static struct ttm_pool_type global_write_combined[TTM_DIM_ORDER];
>       |                             ^~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/ttm/ttm_pool.c:74:29: error: variably modified 'global_uncached' at file scope
>    74 | static struct ttm_pool_type global_uncached[TTM_DIM_ORDER];
>       |                             ^~~~~~~~~~~~~~~
> drivers/gpu/drm/ttm/ttm_pool.c:76:29: error: variably modified 'global_dma32_write_combined' at file scope
>    76 | static struct ttm_pool_type global_dma32_write_combined[TTM_DIM_ORDER];
>       |                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/ttm/ttm_pool.c:77:29: error: variably modified 'global_dma32_uncached' at file scope
>    77 | static struct ttm_pool_type global_dma32_uncached[TTM_DIM_ORDER];
>       |                             ^~~~~~~~~~~~~~~~~~~~~
> 
> Caused by commit
> 
>   322458c2bb1a ("drm/ttm: Reduce the number of used allocation orders for TTM pages")
> 
> PMD_SHIFT is not necessarily a constant on ppc (see
> arch/powerpc/include/asm/book3s/64/pgtable.h).
> 
> I have reverted that commit for today.

Did anyone look into this? I today ran into what looks like the same
compiler error when building a mainline snapshot using a Fedora rawhide
config for ppc64le:

```
 drivers/gpu/drm/ttm/ttm_pool.c:73:29: error: variably modified
'global_write_combined' at file scope
    73 | static struct ttm_pool_type global_write_combined[TTM_DIM_ORDER];
       |                             ^~~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/ttm/ttm_pool.c:74:29: error: variably modified
'global_uncached' at file scope
    74 | static struct ttm_pool_type global_uncached[TTM_DIM_ORDER];
       |                             ^~~~~~~~~~~~~~~
 drivers/gpu/drm/ttm/ttm_pool.c:76:29: error: variably modified
'global_dma32_write_combined' at file scope
    76 | static struct ttm_pool_type
global_dma32_write_combined[TTM_DIM_ORDER];
       |                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/ttm/ttm_pool.c:77:29: error: variably modified
'global_dma32_uncached' at file scope
    77 | static struct ttm_pool_type global_dma32_uncached[TTM_DIM_ORDER];
       |                             ^~~~~~~~~~~~~~~~~~~~~
```

Full build log:

https://copr-be.cloud.fedoraproject.org/results/@kernel-vanilla/mainline/fedora-37-ppc64le/05850588-mainline-mainline-releases/build.log.gz

Ciao, Thorsten