linux-kernel - Re: [PATCH v5 4/7] dmaengine: xilinx_dma: program hardware supported buffer length

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Date:   Mon, 8 Oct 2018 08:46:41 +0200
From:   Andrea Merello <andrea.merello@...il.com>
To:     Vinod <vkoul@...nel.org>
Cc:     dan.j.williams@...el.com, michal.simek@...inx.com,
        appana.durga.rao@...inx.com, dmaengine@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>,
        Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>
Subject: Re: [PATCH v5 4/7] dmaengine: xilinx_dma: program hardware supported
 buffer length

On Tue, Oct 2, 2018 at 4:56 PM Vinod <vkoul@...nel.org> wrote:
>
> On 28-09-18, 08:53, Andrea Merello wrote:
> > On Tue, Sep 18, 2018 at 6:25 PM Vinod <vkoul@...nel.org> wrote:
>
> > > > @@ -964,7 +968,7 @@ static int xilinx_dma_calc_copysize(struct xilinx_dma_chan *chan,
> > > >                                   int size, int done)
> > > >  {
> > > >       size_t copy = min_t(size_t, size - done,
> > > > -                  XILINX_DMA_MAX_TRANS_LEN);
> > > > +                         chan->xdev->max_buffer_len);
> > >
> > > hmm why not add max_buffer_len in patch 1 again, and then use default
> > > len as XILINX_DMA_MAX_TRANS_LEN and add multiple lengths here :)
> >
> > Sorry, I'm not getting your point. Could you please elaborate the "add
> > multiple lengths here" thing ?
>
> IIRC (sorry been travelling and vacation), add
> chan->xdev->max_buffer_len in patch 1 and initialize it to
> XILINX_DMA_MAX_TRANS_LEN. Then in subsequent patches update the length.

Ah ok. IMO introducing max_buffer_len seems more related to what 4/7
does (actually getting the max transfer len from DT,  thus it is not
constant anymore) rather than to what 1/7 does (commonizing the
calculation of transfer len as it is).. This is why I've introduced it
in 4/7..

.. But if you prefer this way, I'll change this :) .. Maybe we can
change 1/7 commit message so that this change looks less off-topic..
But I have not found a very good title yet.. Something like "Prepare
for DMA copy size calculation rework" ?

> --
> ~Vinod