linux-kernel - Re: [PATCH v5 1/2] spi: dw: Add 32 bpw support to DW DMA Controller

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Message-ID: <CAOSNQF3MM6BLi=xs6VJFn9gWHU_00M--akcpsA=Jm=6U=3LZnQ@mail.gmail.com>
Date:   Tue, 11 Apr 2023 20:00:23 +0530
From:   Joy Chakraborty <joychakr@...gle.com>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...el.com>,
        Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
        linux-kernel@...r.kernel.org, manugautam@...gle.com,
        rohitner@...gle.com
Subject: Re: [PATCH v5 1/2] spi: dw: Add 32 bpw support to DW DMA Controller

Hello Andy,

On Tue, Apr 11, 2023 at 7:41 PM Serge Semin <fancer.lancer@...il.com> wrote:
>
> On Tue, Apr 11, 2023 at 03:13:49PM +0300, Andy Shevchenko wrote:
> > On Thu, Mar 30, 2023 at 06:34:49AM +0000, Joy Chakraborty wrote:
> >
> > First of all the Subject is wrong. You are not touching DMA controller.
> > Needs to be rephrased.

Sure, will rephrase this to "SPI DMA Driver" instead of controller.

> >
> > > Add Support for AxSize = 4 bytes configuration from dw dma driver if
> >
> > SPI DMA driver
> >
> > (or something like this, note capital letters for acronyms).
> >
> > > n_bytes i.e. number of bytes per write to fifo is 3 or 4.
> > >
> > > Number of bytes written to fifo per write is depended on the bits/word
> > > configuration being used which the DW core driver translates to n_bytes.
> >
> > ...
> >
> > >  static enum dma_slave_buswidth dw_spi_dma_convert_width(u8 n_bytes)
> > >  {
> > > -   if (n_bytes == 1)
> > > +   switch (n_bytes) {
> > > +   case 1:
> > >             return DMA_SLAVE_BUSWIDTH_1_BYTE;
> > > -   else if (n_bytes == 2)
> > > +   case 2:
> > >             return DMA_SLAVE_BUSWIDTH_2_BYTES;
> > > -
> > > -   return DMA_SLAVE_BUSWIDTH_UNDEFINED;
> >
> > > +   case 3:
> >
> > I'm not sure about this.
>
> This actually makes sense seeing the function argument can have values
> 1, 2, _3_ and 4:
> dws->n_bytes = DIV_ROUND_UP(transfer->bits_per_word, BITS_PER_BYTE);
> transfer->bits_per_word = __F__(master->bits_per_word_mask = SPI_BPW_RANGE_MASK(4, 32));
> ...
> dw_spi_dma_convert_width(dws->n_bytes)
>
> The spi_transfer.bits_per_word field value depends on the
> SPI peripheral device communication protocol requirements which may
> imply the 3-bytes word xfers (even though it's indeed unluckily).
>
> This semantic will also match to what we currently have in the
> IRQ-based SPI-transfer implementation (see dw_writer() and
> dw_reader()).
>
> -Serge(y)
>

Will keep this as is to be similar to dw_writer() / dw_reader() as
explained by Serge(y).

> >
> > > +   case 4:
> > > +           return DMA_SLAVE_BUSWIDTH_4_BYTES;
> > > +   default:
> > > +           return DMA_SLAVE_BUSWIDTH_UNDEFINED;
> > > +   }
> > >  }
> >
> > --
> > With Best Regards,
> > Andy Shevchenko
> >
> >

I shall create another patch series with the same.

Thanks
Joy