lkml.org 
[lkml]   [2016]   [Nov]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2 2/4] spi: spi-fsl-dspi: Fix continuous selection format
On 16-11-21 15:15:41, Stefan Agner wrote:
> On 2016-11-20 21:54, Sanchayan Maity wrote:
> > Current DMA implementation was not handling the continuous selection
> > format viz. SPI chip select would be deasserted even between sequential
> > serial transfers. Use the cs_change variable and correctly set or
> > reset the CONT bit accordingly for case where peripherals require
> > the chip select to be asserted between sequential transfers.
> >
> > Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>
> > ---
> > drivers/spi/spi-fsl-dspi.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
> > index b1ee1f5..41422cd 100644
> > --- a/drivers/spi/spi-fsl-dspi.c
> > +++ b/drivers/spi/spi-fsl-dspi.c
> > @@ -261,6 +261,8 @@ static int dspi_next_xfer_dma_submit(struct fsl_dspi *dspi)
> > dspi->dma->tx_dma_buf[i] = SPI_PUSHR_TXDATA(val) |
> > SPI_PUSHR_PCS(dspi->cs) |
> > SPI_PUSHR_CTAS(0);
> > + if (!dspi->cs_change)
> > + dspi->dma->tx_dma_buf[i] |= SPI_PUSHR_CONT;
> > dspi->tx += tx_word + 1;
> >
> > dma->tx_desc = dmaengine_prep_slave_single(dma->chan_tx,
>
> Other transfer mode use:
>
> if ((dspi->cs_change) && (!dspi->len))
>
> dspi_pushr &= ~SPI_PUSHR_CONT;
>
> which indicates that they only clear SPI_PUSHR_CONT at the very end of a
> transfer... The DMA code currently deselects after every DMA transfer if
> dspi->cs_change is set.
>
> Maybe we should use the helper dspi_data_to_pushr to fill the DMA buffer
> and _clear_ SPI_PUSHR_CONT if necessary like the other transfer modes
> do... Then we can use the for loop to fill the complete buffer and get
> rid of some code dupplication.
>
> I see that dspi_data_to_pushr does move len too, which we did not in the
> DMA case. dspi->len gets incremented only on successful DMA transfer in
> dspi_dma_xfer. However, I wonder if that is not even a bug: We increment
> dspi->tx always, but len only on success. This makes len go off sync
> with regards to the tx pointer which does not help anybody. So lets get
> rid of the update code in dspi_dma_xfer
>

Thanks for the feedback. Using dspi_data_to_pushr really cleans up that
tx path very nicely. Why didn't I see it. Will send a follow up patch
soon after testing again.

- Sanchayan.

\
 
 \ /
  Last update: 2016-11-22 07:21    [W:2.147 / U:0.016 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site