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

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Message-ID: <ZDVyyoN71cB7dvWW@smile.fi.intel.com>
Date:   Tue, 11 Apr 2023 17:46:34 +0300
From:   Andy Shevchenko <andriy.shevchenko@...el.com>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Joy Chakraborty <joychakr@...gle.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

On Tue, Apr 11, 2023 at 05:11:15PM +0300, Serge Semin 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:

...

> > > -	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()).

Nice, but we have DMA_SLAVE_BUSWIDTH_3_BYTES definition for that. Why we don't
use it?

> > > +	case 4:
> > > +		return DMA_SLAVE_BUSWIDTH_4_BYTES;
> > > +	default:
> > > +		return DMA_SLAVE_BUSWIDTH_UNDEFINED;
> > > +	}

-- 
With Best Regards,
Andy Shevchenko