Re: [PATCH] drm/imagination: Kconfig: add 'PAGE_SIZE=4K' dependency

[Matt Coster <Matt.Coster@imgtec.com>]

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Hi, thanks for the patch!

On 28/02/2024 01:23, Lu Yao wrote:
> When 'PAGE_SIZE=64K',the following compilation error occurs:
> "
>   ../drivers/gpu/drm/imagination/pvr_fw_mips.c: In function
> ‘pvr_mips_fw_process’:
>   ../drivers/gpu/drm/imagination/pvr_fw_mips.c:140:60: error: array
> subscript 0 is outside the bounds of an interior zero-length array
> ‘dma_addr_t[0]’ {aka ‘long long unsigned int[]’}
> [-Werror=zero-length-bounds]
>   140 |   boot_data->pt_phys_addr[page_nr] =
> mips_data->pt_dma_addr[src_page_nr] +
> ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~
>   In file included from ../drivers/gpu/drm/imagination/pvr_fw_mips.c:6:
>   ../drivers/gpu/drm/imagination/pvr_fw_mips.h:30:13: note: while
> referencing ‘pt_dma_addr’
>    30 |  dma_addr_t pt_dma_addr[PVR_MIPS_PT_PAGE_COUNT];
> "
> 
> This is because 'PVR_MIPS_PT_PAGE_COUNT' is defined as
> '(ROGUE_MIPSFW_MAX_NUM_PAGETABLE_PAGES * ROGUE_MIPSFW_PAGE_SIZE_4K) \
>>> PAGE_SHIFT', and under the above conditions, 'PAGE_SHIFT' is '16',
> 'ROGUE_MIPSFW_MAX_NUM_PAGETABLE_PAGES' is '4','ROGUE_MIPSFW_PAGE_SIZE_4K'
> is '4096',so 'PVR_MIPS_PT_PAGE_COUNT' is '0' causing the member
> 'pt_dma_addr' to be incorrectly defined.

The whole MIPS page table system is supposed to be host page-size
agnostic. In practice, we don’t regularly test on non-4K platforms so
this may well be broken in subtle or not-so-subtle (as in this instance)
ways. There has been at least some testing with 64K host pages – the
configs from TI for the AM62-SK dev boards have that as the default (or
at least they did when we started working with them).

I’m loathed to accept this patch without at least investigating how deep
the problems go; the true fix here should be to fix the problems causing
this build error rather than just gating off non-4K hosts.

I’ll have a dig this afternoon to see what I can find. Did you try
anything to fix this yourself? It would be nice to not duplicate effort
on this if you have.

Cheers,
Matt

> Signed-off-by: Lu Yao <yaolu@kylinos.cn>
> ---
>  drivers/gpu/drm/imagination/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/imagination/Kconfig b/drivers/gpu/drm/imagination/Kconfig
> index 3bfa2ac212dc..e585922f634d 100644
> --- a/drivers/gpu/drm/imagination/Kconfig
> +++ b/drivers/gpu/drm/imagination/Kconfig
> @@ -3,7 +3,7 @@
>  
>  config DRM_POWERVR
>  	tristate "Imagination Technologies PowerVR (Series 6 and later) & IMG Graphics"
> -	depends on ARM64
> +	depends on (ARM64 && ARM64_PAGE_SHIFT=12)
>  	depends on DRM
>  	depends on PM
>  	select DRM_EXEC

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