Re: [PATCH v2 06/10] drm/ingenic: Set DMA descriptor chain address in probe

2020-07-01 Thread Paul Cercueil

Hi Sam,

Le mar. 30 juin 2020 à 13:44, Sam Ravnborg  a écrit 
:

Hi Paul.

On Tue, Jun 30, 2020 at 01:52:06AM +0200, Paul Cercueil wrote:
 The address of the DMA descriptor never changes. It can therefore 
be set

 in the probe function.

 Signed-off-by: Paul Cercueil 
 ---

 Notes:
 v2: No change

  drivers/gpu/drm/ingenic/ingenic-drm-drv.c | 5 +++--
  1 file changed, 3 insertions(+), 2 deletions(-)

 diff --git a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c 
b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c

 index 924c8daf071a..f7b0c5dc8cd8 100644
 --- a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
 +++ b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
 @@ -358,8 +358,6 @@ static void 
ingenic_drm_crtc_atomic_flush(struct drm_crtc *crtc,

ingenic_drm_crtc_update_ctrl(priv, finfo);

clk_set_rate(priv->pix_clk, state->adjusted_mode.clock * 1000);
 -
 -  regmap_write(priv->map, JZ_REG_LCD_DA0, priv->dma_hwdesc->next);
}

if (event) {
 @@ -757,6 +755,9 @@ static int ingenic_drm_probe(struct 
platform_device *pdev)

}
}

 +  /* Set address of our DMA descriptor chain */
 +  regmap_write(priv->map, JZ_REG_LCD_DA0, priv->dma_hwdesc_phys);
 +



What is the purpose of this code after the assignment was moved:

static int ingenic_drm_probe(struct platform_device *pdev)
{
...
priv->dma_hwdesc->next = priv->dma_hwdesc_phys;

I do not see ->next used anymore.
Could this assignment be dropped?


And the following line:
priv->dma_hwdesc->id = 0xdeafbead;

I can only see ->id be assingned, it is never referenced??

Maybe this is all related to the structure assumed by the data pointed
to by JZ_REG_LCD_DA0?


As its name suggests, 'dma_hwdesc' points to a DMA hardware descriptor. 
Setting ->next sets the address of the next descriptor (which is itself 
since we only use one descriptor). The 'id' field will be copied by the 
hardware to a register when the DMA descriptor is loaded, so we can 
know from userspace (debugfs) what DMA descriptors are loaded by 
looking up the IDs.


-Paul


Sam


ret = drm_dev_register(drm, 0);
if (ret) {
dev_err(dev, "Failed to register DRM driver\n");
 --
 2.27.0

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Re: [PATCH v2 06/10] drm/ingenic: Set DMA descriptor chain address in probe

2020-06-30 Thread Sam Ravnborg
Hi Paul.

On Tue, Jun 30, 2020 at 01:52:06AM +0200, Paul Cercueil wrote:
> The address of the DMA descriptor never changes. It can therefore be set
> in the probe function.
> 
> Signed-off-by: Paul Cercueil 
> ---
> 
> Notes:
> v2: No change
> 
>  drivers/gpu/drm/ingenic/ingenic-drm-drv.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c 
> b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> index 924c8daf071a..f7b0c5dc8cd8 100644
> --- a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> +++ b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> @@ -358,8 +358,6 @@ static void ingenic_drm_crtc_atomic_flush(struct drm_crtc 
> *crtc,
>   ingenic_drm_crtc_update_ctrl(priv, finfo);
>  
>   clk_set_rate(priv->pix_clk, state->adjusted_mode.clock * 1000);
> -
> - regmap_write(priv->map, JZ_REG_LCD_DA0, priv->dma_hwdesc->next);
>   }
>  
>   if (event) {
> @@ -757,6 +755,9 @@ static int ingenic_drm_probe(struct platform_device *pdev)
>   }
>   }
>  
> + /* Set address of our DMA descriptor chain */
> + regmap_write(priv->map, JZ_REG_LCD_DA0, priv->dma_hwdesc_phys);
> +


What is the purpose of this code after the assignment was moved:

static int ingenic_drm_probe(struct platform_device *pdev)
{
...
priv->dma_hwdesc->next = priv->dma_hwdesc_phys;

I do not see ->next used anymore.
Could this assignment be dropped?


And the following line:
priv->dma_hwdesc->id = 0xdeafbead;

I can only see ->id be assingned, it is never referenced??

Maybe this is all related to the structure assumed by the data pointed
to by JZ_REG_LCD_DA0?

Sam

>   ret = drm_dev_register(drm, 0);
>   if (ret) {
>   dev_err(dev, "Failed to register DRM driver\n");
> -- 
> 2.27.0
> 
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> dri-devel@lists.freedesktop.org
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