Hi, Yongqiang:

On Wed, 2019-03-27 at 14:19 +0800, yongqiang....@mediatek.com wrote:
> From: Yongqiang Niu <yongqiang....@mediatek.com>
> 
> This patch add ddp write register common api
> this is preparation patch for ovl/ovl_2l direct link
> usecase.
> in that case, we need this funtion to set one bit of ovl_2l
> register

The reason is so strange. You could grep 'readl' in mediatek drm driver,
and you would find that many place need this function. 

> 
> Signed-off-by: Yongqiang Niu <yongqiang....@mediatek.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c | 11 +++++++++++
>  drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.h |  4 ++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c 
> b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
> index afd6ca2..72288b4 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
> @@ -84,6 +84,17 @@
>  #define DITHER_ADD_LSHIFT_G(x)                       (((x) & 0x7) << 4)
>  #define DITHER_ADD_RSHIFT_G(x)                       (((x) & 0x7) << 0)
>  
> +void mtk_ddp_write_mask(unsigned int value,
> +                     struct mtk_ddp_comp *comp,
> +                     unsigned int offset,
> +                     unsigned int mask)
> +{
> +     unsigned int tmp = readl(comp->regs + offset);
> +
> +     tmp = (tmp & ~mask) | (value & mask);

Why not just place this calculation into writel()?

Regards,
CK

> +     writel(tmp, comp->regs + offset);
> +}
> +
>  void mtk_dither_set(struct mtk_ddp_comp *comp, unsigned int bpc,
>                   unsigned int CFG)
>  {
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.h 
> b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.h
> index 20e8061..ed715ff 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.h
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.h
> @@ -198,5 +198,9 @@ int mtk_ddp_comp_init(struct device *dev, struct 
> device_node *comp_node,
>  void mtk_ddp_comp_unregister(struct drm_device *drm, struct mtk_ddp_comp 
> *comp);
>  void mtk_dither_set(struct mtk_ddp_comp *comp, unsigned int bpc,
>                   unsigned int CFG);
> +void mtk_ddp_write_mask(unsigned int value,
> +                     struct mtk_ddp_comp *comp,
> +                     unsigned int offset,
> +                     unsigned int mask);
>  
>  #endif /* MTK_DRM_DDP_COMP_H */


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