RE: [PATCH v2 1/4] spi: spi-mem: Add the spi_set_xfer_bpw function

[Chuanhua Han <chuanhua.han@xxxxxxx>]

> -----Original Message-----
> From: Esben Haabendal <esbenhaabendal@xxxxxxxxx> On Behalf Of Esben
> Haabendal
> Sent: 2018年9月30日 18:18
> To: Boris Brezillon <boris.brezillon@xxxxxxxxxxx>
> Cc: Chuanhua Han <chuanhua.han@xxxxxxx>; broonie@xxxxxxxxxx;
> linux-spi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2 1/4] spi: spi-mem: Add the spi_set_xfer_bpw function
> 
> Boris Brezillon <boris.brezillon@xxxxxxxxxxx> writes:
> 
> > Hi Chuanhua,
> >
> > On Sun, 30 Sep 2018 17:25:32 +0800
> > Chuanhua Han <chuanhua.han@xxxxxxx> wrote:
> >
> >> Before we add this spi_transfer to the spi_message chain table, we
> >> need bits_per_word_mask based on spi_control to set the bits_per_word
> >> of this spi_transfer.
> >
> > Let's make it clearer: this is wrong. The spi-mem protocol is just
> > using bytes, not custom size words. Fix the fsl-dspi driver if needed,
> > but don't try to adjust xfer->bits_per_word in spi-mem.c, because this
> > is inappropriate.
> 
> I don't think there is a "fix" needed in fsl-dspi driver for this.
> 
> I am not sure, but I think that what Han is trying to achieve here is better
> performance.
> And wile the XSPI mode does provide better performance for sending one
> 32 bit word, than normal mode providees for sending 4 x 8 bit words.
> But as you say, this is wrong.
> 
> To improve performance, the fsl-dspi driver should be fixed to work in DMA
> mode.  Implementation of erratum A-011218 is necessary in order to use
> DSPI DMA mode on LS1021A.
> I was planning to work on that, but haven't had the time for it.
> So if you want better performance for spi-mem on LS1021A DSPI, please work
> on this.
> 
> /Esben
Hi，
Another colleague is responsible for the DMA transmission of dspi.
I am not clear about it. I just fix the transmission of XSPI mode with several patches. 
Thank you for your comments.