linux-kernel - Re: [PATCH v2 0/3] dmaengine: Add support for immediate commands

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Message-ID: <Y3FudBqc1vQ8fEgU@matsya>
Date:   Mon, 14 Nov 2022 03:53:48 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Sireesh Kodali <sireeshkodali1@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org,
        ~postmarketos/upstreaming@...ts.sr.ht
Subject: Re: [PATCH v2 0/3] dmaengine: Add support for immediate commands

On 11-11-22, 10:42, Sireesh Kodali wrote:
> On Fri Nov 4, 2022 at 6:10 PM IST, Vinod Koul wrote:
> > On 27-10-22, 10:44, Sireesh Kodali wrote:
> > > The IPA v2.x block, found on some older Qualcomm SoCs, uses BAM DMA to
> > > send and receive packets from the AP. It also uses BAM to receive
> > > commands from the AP (and possibly the modem). These commands are
> > > encoded as "Immediate Commands". They vary from regular BAM DMA
> > > commands. Adding support for immediate commands is trivial, but requires
> > > also adding Immediate Commands to the dmaengine API, which is what this
> > > patch series does.
> >
> > Can you explain a bit more. I understand you need "Immediate Commands"
> > but am really reluctant to add another interface to support a specific
> > use case
> >
> 
> Apologies for the delayed response
> 
> BAM supports both regular commands, and "immediate commands". Currently,
> commands are used by the Qualcom NAND chip driver, while "immediate
> commands" are intended to be used by the (yet to be mainlined) IPA
> driver. From the BAM driver perspective, both immediate and regular
> commands are simply a matter of setting the appropriate flag in the
> descriptor. I don't have access to the documentation on BAM to know
> exactly how these two modes differ, however I do know they are not
> interchangable. If a different API is suggested, I can change the
> implementation as needed.

Ok, can you please explain what is meant by 'regular' cmd and
'immediate', lets see what is required here

-- 
~Vinod