Re: [PATCH v1] misc: fastrpc: Free DMA handles for RPC calls with no arguments

[Ekansh Gupta]

On 9/26/2023 3:57 PM, Srinivas Kandagatla wrote:
> Thanks Ekansh for this patch.
>
> few comments below
>
> On 31/08/2023 07:23, Ekansh Gupta wrote:
> > The FDs for DMA handles to be freed is updated in fdlist by DSP over
>
> So the dsp is updating the fd list after invoke?
Yes, correct. DSP updates this fd list when the buffer is no longer 
needed by the user PD.
> > a remote call. This holds true even for remote calls with no
> > arguments. To handle this, get_args and put_args are needed to
> > be called for remote calls with no arguments also as fdlist
> > is allocated in get_args and FDs updated in fdlist is freed
> > in put_args.
> >
> > Signed-off-by: Ekansh Gupta <quic_ekangupt@xxxxxxxxxxx>
> > ---
> >   drivers/misc/fastrpc.c | 22 +++++++++-------------
> >   1 file changed, 9 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> > index 9666d28..e6df66e 100644
> > --- a/drivers/misc/fastrpc.c
> > +++ b/drivers/misc/fastrpc.c
> > @@ -1153,11 +1153,9 @@ static int fastrpc_internal_invoke(struct 
> > fastrpc_user *fl,  u32 kernel,
> >       if (IS_ERR(ctx))
> >           return PTR_ERR(ctx);
> > -    if (ctx->nscalars) {
>
> Why do we need to remove this check?
> fastrpc_internal_invoke will have nscalars set before calling. and we 
> are not dealing with fdlist in fastrpc_get_args(), so am not sure what 
> this change is helping with.
Memory for fdlist is allocated as part of fastrpc_get_args. The reason 
to add this change is that fdlist can be updated by DSP over a call with 
no remote arguments, for this call, there should be some fdlist 
allocated so the DSP can update the list if needed. Same apply for 
fastrpc_put_args also as when DSP updates fdlist for any remote call 
with no arguments, the maps corresponding to the fdlist should be freed.
> > -        err = fastrpc_get_args(kernel, ctx);
> > -        if (err)
> > -            goto bail;
> > -    }
> > +    err = fastrpc_get_args(kernel, ctx);
> > +    if (err)
> > +        goto bail;
> >       /* make sure that all CPU memory writes are seen by DSP */
> >       dma_wmb();
> > @@ -1181,14 +1179,12 @@ static int fastrpc_internal_invoke(struct 
> > fastrpc_user *fl,  u32 kernel,
> >       if (err)
> >           goto bail;
> > -    if (ctx->nscalars) {
> > -        /* make sure that all memory writes by DSP are seen by CPU */
> > -        dma_rmb();
> > -        /* populate all the output buffers with results */
> > -        err = fastrpc_put_args(ctx, kernel);
> > -        if (err)
> > -            goto bail;
> > -    }
> > +    /* make sure that all memory writes by DSP are seen by CPU */
> > +    dma_rmb();
> > +    /* populate all the output buffers with results */
>
> A comment about fdlist here would be really useful
Sure, I will add a comment in the next patch. Do you suggest to add 
comment here or inside fastrpc_put_args function:
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/misc/fastrpc.c#n1092
> > +    err = fastrpc_put_args(ctx, kernel);
> > +    if (err)
> > +        goto bail;
> >   bail:
> >       if (err != -ERESTARTSYS && err != -ETIMEDOUT) {