linux-kernel - Re: [PATCH 4/8] spi: dw-dma: Move DMA transfers submission to the channels prep methods

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Date:   Fri, 31 Jul 2020 15:46:46 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     Serge Semin <fancer.lancer@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Georgy Vlasov <Georgy.Vlasov@...kalelectronics.ru>,
        Ramil Zaripov <Ramil.Zaripov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Feng Tang <feng.tang@...el.com>, Vinod Koul <vkoul@...nel.org>,
        <linux-spi@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/8] spi: dw-dma: Move DMA transfers submission to the
 channels prep methods

On Fri, Jul 31, 2020 at 12:15:28PM +0300, Andy Shevchenko wrote:
> On Fri, Jul 31, 2020 at 10:59:49AM +0300, Serge Semin wrote:
> > Indeed we can freely move the dmaengine_submit() method invocation and the
> > Tx and Rx busy flag setting into the DMA Tx/Rx prepare methods. By doing
> > so first we implement another preparation before adding the one-by-one DMA
> > SG entries transmission, second we now have the dma_async_tx_descriptor
> > descriptor used locally only in the new DMA transfers submitition methods,
> > which makes the code less complex with no passing around the DMA Tx
> > descriptors, third we make the generic transfer method more readable, where
> > now the functionality of submission, execution and wait procedures is
> > transparently split up instead of having a preparation, intermixed
> > submission/execution and wait procedures. While at it we also add the
> > dmaengine_submit() return value test. It has been unnecessary for
> > DW DMAC, but should be done to support the generic DMA interface.
> > 
> > Note since the DMA channels preparation methods are now responsible for
> > the DMA transactions submission, we also rename them to
> > dw_spi_dma_submit_{tx,rx}().
> 
> ...
> 
> > +	cookie = dmaengine_submit(txdesc);
> > +	ret = dma_submit_error(cookie);
> > +	if (!ret)
> 

> Use traditional pattern
> 	if (ret)
> 		return ret;
> 
> Same for below.

Ok.

> 
> > +		set_bit(TX_BUSY, &dws->dma_chan_busy);
> > +
> > +	return ret;
> 
> ...
> 

> > -	if (!xfer->rx_buf)
> > -		return NULL;
> 
> This seems not related.

I moved it to the upper level for the methods better maintainability.

-Sergey

> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>