Re: [PATCH v3] pmdomain: imx8m-blk-ctrl: Serialize power on/off across sibling domains

[Frank Li]

On Mon, Sep 21, 2026 at 07:03:34PM +0900, Ming Qian wrote:
> On i.MX8MP the VPU blk-ctrl exposes G1, G2 and VC8000E as three separate
> genpds, each serialized only by its own genpd lock, so their power_on and
> power_off callbacks can run concurrently on SMP.
>
> The sequences are not independent: they share the VPUMIX bus domain, the
> VPU_NOC and the ADB400 handshake. On power up the GPC cannot ack-verify
> the ADB400 handshake - the ack only completes once blk-ctrl sets the bus
> clk-en bit - so it just waits a fixed delay instead of polling hskack. A
> sibling transition landing inside another domain's reset window disturbs
> that shared clock and handshake timing, the victim's reset does not take
> effect, and its block registers read back all zeros: the decoder times
> out or the encoder fails its format check.
>
> Serialize the blk-ctrl reset sequence with a per-blk-ctrl mutex; the
> driver deliberately avoids a genpd hierarchy, so the genpd core gives no
> cross-sibling serialization.
>
> Fixes: a1a5f15f7f6c ("soc: imx: imx8m-blk-ctrl: add i.MX8MP VPU blk ctrl")
> Signed-off-by: Ming Qian <ming.qian@xxxxxxxxxxx>
> ---
> Problem:
> On i.MX8MP, running the VC8000E encoder and the G1/G2 decoders
> concurrently rarely and non-deterministically leaves a VPU stuck in
> reset: its block registers read back all zeros. A decoder then times out
> or the encoder fails its format check.
>
> Root cause:
> The VPU blk-ctrl exposes G1, G2 and VC8000E as three separate genpds,
> serialized only by the per-genpd lock, so on SMP their power_on/power_off
> callbacks can run concurrently. The sequences share the VPUMIX bus
> domain, the VPU_NOC and the ADB400 handshake. On power up the GPC does
> not ack-verify the ADB400 handshake - the ack only completes once
> blk-ctrl sets the bus clk-en bit - so it just waits a fixed delay. A
> sibling transition landing inside another domain's reset window disturbs
> that shared clock and handshake timing, the victim's reset fails to take
> effect, and its block is left in reset with registers reading zero.
>
> Fix:
> Serialize the blk-ctrl reset sequence with a per-blk-ctrl mutex, so a
> sibling domain cannot run its sequence while another is inside its reset
> window. The driver deliberately avoids a genpd hierarchy, so the genpd
> core provides no cross-sibling serialization.
>
> Test:
> i.MX8MP, Android 6.18 kernel, concurrent H.264 decode and encode. Without
> this patch the failure reproduces within one to two hours. With it the
> same test ran overnight, over 14 hours, without a single occurrence.
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>