linux-kernel - Re: [PATCH v4 2/7] dmaengine: xilinx_dma: in axidma slave_sg and dma

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Date:   Thu, 30 Aug 2018 10:11:53 +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-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 v4 2/7] dmaengine: xilinx_dma: in axidma slave_sg and
 dma_cylic mode align split descriptors

On Wed, Aug 29, 2018 at 10:12 AM Andrea Merello
<andrea.merello@...il.com> wrote:
>
> On Mon, Aug 27, 2018 at 7:30 AM Vinod <vkoul@...nel.org> wrote:
> >
> > On 02-08-18, 16:10, Andrea Merello wrote:
> >
> > s/cylic/cyclic in patch title
>
> OK
>
> > > Whenever a single or cyclic transaction is prepared, the driver
> > > could eventually split it over several SG descriptors in order
> > > to deal with the HW maximum transfer length.
> > >
> > > This could end up in DMA operations starting from a misaligned
> > > address. This seems fatal for the HW if DRE is not enabled.
> >
> > DRE?
>
> Stands for "Data Realignment Engine". I will add this string nearby
> the acronym..
>
> > >
> > > This patch eventually adjusts the transfer size in order to make sure
> > > all operations start from an aligned address.
> > >
> > > Cc: Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>
> > > Signed-off-by: Andrea Merello <andrea.merello@...il.com>
> > > Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>
> > > ---
> > > Changes in v2:
> > >         - don't introduce copy_mask field, rather rely on already-esistent
> > >           copy_align field. Suggested by Radhey Shyam Pandey
> > >         - reword title
> > > Changes in v3:
> > >       - fix bug introduced in v2: wrong copy size when DRE is enabled
> > >       - use implementation suggested by Radhey Shyam Pandey
> > > Changes in v4:
> > >       - rework on the top of 1/6
> > > ---
> > >  drivers/dma/xilinx/xilinx_dma.c | 22 ++++++++++++++++++----
> > >  1 file changed, 18 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
> > > index a3aaa0e34cc7..aaa6de8a70e4 100644
> > > --- a/drivers/dma/xilinx/xilinx_dma.c
> > > +++ b/drivers/dma/xilinx/xilinx_dma.c
> > > @@ -954,15 +954,28 @@ static int xilinx_dma_alloc_chan_resources(struct dma_chan *dchan)
> > >
> > >  /**
> > >   * xilinx_dma_calc_copysize - Calculate the amount of data to copy
> > > + * @chan: Driver specific DMA channel
> > >   * @size: Total data that needs to be copied
> > >   * @done: Amount of data that has been already copied
> > >   *
> > >   * Return: Amount of data that has to be copied
> > >   */
> > > -static int xilinx_dma_calc_copysize(int size, int done)
> > > +static int xilinx_dma_calc_copysize(struct xilinx_dma_chan *chan,
> > > +                                 int size, int done)
> >
> > please align with opening brace
>
> OK

Sorry for getting back on this.
I've checked it, but it seems already aligned with opening brace in
the original e-mail text I've sent. (4 tabs + 4 spaces).


> > >  {
> > > -     return min_t(size_t, size - done,
> > > +     size_t copy = min_t(size_t, size - done,
> > >                    XILINX_DMA_MAX_TRANS_LEN);
> > > +
> > > +     if ((copy + done < size) &&
> > > +         chan->xdev->common.copy_align) {
> > > +             /*
> > > +              * If this is not the last descriptor, make sure
> > > +              * the next one will be properly aligned
> > > +              */
> > > +             copy = rounddown(copy,
> > > +                              (1 << chan->xdev->common.copy_align));
> > > +     }
> > > +     return copy;
> > >  }
> > >
> > >  /**
> > > @@ -1804,7 +1817,7 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_slave_sg(
> > >                        * Calculate the maximum number of bytes to transfer,
> > >                        * making sure it is less than the hw limit
> > >                        */
> > > -                     copy = xilinx_dma_calc_copysize(sg_dma_len(sg),
> > > +                     copy = xilinx_dma_calc_copysize(chan, sg_dma_len(sg),
> > >                                                       sg_used);
> > >                       hw = &segment->hw;
> > >
> > > @@ -1909,7 +1922,8 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_dma_cyclic(
> > >                        * Calculate the maximum number of bytes to transfer,
> > >                        * making sure it is less than the hw limit
> > >                        */
> > > -                     copy = xilinx_dma_calc_copysize(period_len, sg_used);
> > > +                     copy = xilinx_dma_calc_copysize(chan,
> > > +                                                     period_len, sg_used);
> > >                       hw = &segment->hw;
> > >                       xilinx_axidma_buf(chan, hw, buf_addr, sg_used,
> > >                                         period_len * i);
> > > --
> > > 2.17.1
> >
> > --
> > ~Vinod