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SubjectRe: [PATCH v2 06/10] drm/ingenic: Set DMA descriptor chain address in probe
Hi Sam,

Le mar. 30 juin 2020 à 13:44, Sam Ravnborg <sam@ravnborg.org> 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 <paul@crapouillou.net>
>> ---
>>
>> 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
>>
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel


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