Re: [PATCH v9 05/15] iommu/mediatek: Add device_link between the consumer and the larb devices

[AngeloGioacchino Del Regno]

Il 12/11/21 11:54, Yong Wu ha scritto:
> MediaTek IOMMU-SMI diagram is like below. all the consumer connect with
> smi-larb, then connect with smi-common.
>
>          M4U
>           |
>      smi-common
>           |
>    -------------
>    |         |    ...
>    |         |
> larb1     larb2
>    |         |
> vdec       venc
>
> When the consumer works, it should enable the smi-larb's power which
> also need enable the smi-common's power firstly.
>
> Thus, First of all, use the device link connect the consumer and the
> smi-larbs. then add device link between the smi-larb and smi-common.
>
> This patch adds device_link between the consumer and the larbs.
>
> When device_link_add, I add the flag DL_FLAG_STATELESS to avoid calling
> pm_runtime_xx to keep the original status of clocks. It can avoid two
> issues:
> 1) Display HW show fastlogo abnormally reported in [1]. At the beggining,
> all the clocks are enabled before entering kernel, but the clocks for
> display HW(always in larb0) will be gated after clk_enable and clk_disable
> called from device_link_add(->pm_runtime_resume) and rpm_idle. The clock
> operation happened before display driver probe. At that time, the display
> HW will be abnormal.
>
> 2) A deadlock issue reported in [2]. Use DL_FLAG_STATELESS to skip
> pm_runtime_xx to avoid the deadlock.
>
> Corresponding, DL_FLAG_AUTOREMOVE_CONSUMER can't be added, then
> device_link_removed should be added explicitly.
>
> Meanwhile, Currently we don't have a device connect with 2 larbs at the
> same time. Disallow this case, print the error log.
>
> [1] https://lore.kernel.org/linux-mediatek/1564213888.22908.4.camel@mhfsdcap03/
> [2] https://lore.kernel.org/patchwork/patch/1086569/
>
> Suggested-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
> Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
> Tested-by: Frank Wunderlich <frank-w@xxxxxxxxxxxxxxx> # BPI-R2/MT7623

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>