linux-kernel - Re: [PATCH v8 01/11] dmaengine: Add DMA_PREP_LOCK/DMA_PREP

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Message-ID: <CAMRc=MfqYiuLaz_28nE+5QSdiG-MyTk885HSO4OYz8Wf4myfJQ@mail.gmail.com>
Date: Fri, 21 Nov 2025 18:31:59 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Vinod Koul <vkoul@...nel.org>, Jonathan Corbet <corbet@....net>, 
	Thara Gopinath <thara.gopinath@...il.com>, Herbert Xu <herbert@...dor.apana.org.au>, 
	"David S. Miller" <davem@...emloft.net>, Udit Tiwari <quic_utiwari@...cinc.com>, 
	Daniel Perez-Zoghbi <dperezzo@...cinc.com>, Md Sadre Alam <mdalam@....qualcomm.com>, 
	dmaengine@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	linux-crypto@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v8 01/11] dmaengine: Add DMA_PREP_LOCK/DMA_PREP_UNLOCK flags

On Fri, Nov 21, 2025 at 5:36 PM Dmitry Baryshkov
<dmitry.baryshkov@....qualcomm.com> wrote:
>
> >
> > The flag has to be passed to the BAM driver at the time of calling of
> > dmaengine_prep_slave_sg() and attrs seems to be the only way with the
> > current interface. Off the top of my head: we could extend struct
> > scatterlist to allow passing some arbitrary driver data but that
> > doesn't sound like a good approach.
>
> Can we use DMA metadata in order to pass the lock / unlock flags
> instead? I might be missing something, but the LOCK / UNLOCK ops defined
> in this patchset seem to be too usecase-specific. Using metadata seems
> to allow for this kind of driver-specific sidechannel.
>

I'll look into it, thanks.

Bart