[PATCH v2 2/2] drm/omap: partial workaround for DRA7xx DMM errata i878

[Tomi Valkeinen]

On 22/03/18 15:42, Peter Ujfalusi wrote:
> From: Tomi Valkeinen <tomi.valkeinen at ti.com>
> 
> Errata i878 says that MPU should not be used to access RAM and DMM at
> the same time. As it's not possible to prevent MPU accessing RAM, we
> need to access DMM via a proxy.
> 
> This patch changes DMM driver to access DMM registers via sDMA. Instead
> of doing a normal readl/writel call to read/write a register, we use
> sDMA to copy 4 bytes from/to the DMM registers.
> 
> This patch provides only a partial workaround for i878, as not only DMM
> register reads/writes are affected, but also accesses to the DMM mapped
> buffers (framebuffers, usually).
> 
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
> ---
>  drivers/gpu/drm/omapdrm/omap_dmm_priv.h  |   8 ++
>  drivers/gpu/drm/omapdrm/omap_dmm_tiler.c | 153 ++++++++++++++++++++++++++++++-
>  2 files changed, 159 insertions(+), 2 deletions(-)
> 


> +	dmm->wa_dma_chan = dma_request_channel(mask, NULL, NULL);
> +	if (!dmm->wa_dma_chan) {
> +		dma_free_coherent(dmm->dev, 4, dmm->wa_dma_data, dmm->wa_dma_handle);

This and the other free below should use sizeof(u32) as the alloc does.
And I guess device_prep_dma_memcpy() too. Perhaps a #define would be
best here. DMM_REG_SIZE? I can do this change when applying, if you agree.

 Tomi

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