Re: [PATCH v2] misc: fastrpc: Drop unhandled DSP PD exit notification

[Shawn Guo <shengchao.guo@oss.qualcomm.com>]

On Tue, Jul 28, 2026 at 04:06:50PM +0100, Srinivas Kandagatla wrote:
> 
> 
> On 7/28/26 8:38 AM, Shawn Guo wrote:
> > Newer DSP firmware implements a PD (Protection Domain) notification
> > framework that sends PD state notifications upon request. The PD exit
> > notification is unconditionally sent by the DSP with a fixed sentinel
> > 0xABCDABCD in the context field.
> > 
> > fastrpc_rpmsg_callback() treats every inbound message as an invoke
> > response, so the sentinel is masked and shifted like any real response
> > ((0xABCDABCD & 0xFF0) >> 4 == 188) and looked up in the channel's
> > context idr.
> > 
> > This is not merely cosmetic. In the common case idr slot 188 is empty,
> > the lookup fails, and the driver only logs a spurious "No context ID
> > matches response" error on every teardown. But the context idr is shared
> > by every protection domain and the listener thread on the channel and is
> > filled cyclically over [1, FASTRPC_CTX_MAX]. If slot 188 holds a live
> > context when the sentinel arrives, the sentinel's return value is written
> > into that unrelated in-flight invocation and it is completed early.
> > 
> > Since neither the fastrpc library nor the driver supports the DSP PD
> > notification framework, it is safe to drop the PD exit notification
> > before it is ever turned into a context lookup. This removes both the
> > log spam and the mis-completion race. A genuine response can never be
> > masked: a real context is (idr_index << 4) | pd (at most 0xFF3) and
> > can never equal the sentinel.
> > 
> > Assisted-by: Claude:claude-opus-4-8
> > Reviewed-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
> > Signed-off-by: Shawn Guo <shengchao.guo@oss.qualcomm.com>
> > ---
> 
> Does not apply to linux-next, can you rebase it pl.

Hmm, the patch was based on next-20260727 and still applies to
next-20260728. I pushed a branch based on next-20260728 for your
reference here [1].

Shawn

[1] https://github.com/shawngsc/linux/commits/next-20260728-nord-fastrpc-v2