Re: [PATCH v9 03/11] dmaengine: qcom: bam_dma: implement support for BAM locking

[Vinod Koul <vkoul@kernel.org>]

On 23-12-25, 13:35, Bartosz Golaszewski wrote:
> On Tue, Dec 23, 2025 at 11:45 AM Vinod Koul <vkoul@kernel.org> wrote:
> >
> > On 17-12-25, 15:31, Bartosz Golaszewski wrote:
> > > On Tue, Dec 16, 2025 at 4:11 PM Vinod Koul <vkoul@kernel.org> wrote:
> >
> > > >
> > > > I am trying to understand what the flag refers to and why do you need
> > > > this.. What is the problem that lock tries to solve
> > > >
> > >
> > > In the DRM use-case the TA will use the QCE simultaneously with linux.
> >
> > TA..?
> 
> Trusted Application, the one to which we offload the decryption of the
> stream. That's not really relevant though.
> 
> >
> > > It will perform register I/O with DMA using the BAM locking mechanism
> > > for synchronization. Currently linux doesn't use BAM locking and is
> > > using CPU for register I/O so trying to access locked registers will
> > > result in external abort. I'm trying to make the QCE driver use DMA
> > > for register I/O AND use BAM locking. To that end: we need to pass
> > > information about wanting the command descriptor to contain the
> > > LOCK/UNLOCK flag (this is what we set here in the hardware descriptor)
> > > from the QCE driver to the BAM driver. I initially used a global flag.
> > > Dmitry said it's too Qualcomm-specific and to use metadata instead.
> > > This is what I did in this version.
> >
> > Okay, how will client figure out should it set the lock or not? What are
> > the conditions where the lock is set or not set by client..?
> >
> 
> I'm not sure what you refer to as "client". The user of the BAM engine
> - the crypto driver? If so - we convert it to always lock/unlock
> assuming the TA *may* use it and it's better to be safe. Other users
> are not affected.

Client are users of dmaengine. So how does the crypto driver figure out
when to lock/unlock. Why not do this always...?

-- 
~Vinod