[U-Boot] [PATCH 1/4 v2] spi: spi-mem: Use 2 SPI messages instead of a single full-duplex one

[Miquel Raynal]

Hi Stefan,

Stefan Roese <sr at denx.de> wrote on Thu, 9 Aug 2018 07:24:14 +0200:

> Hi Miquel,
> 
> On 08.08.2018 10:56, Miquel Raynal wrote:
> > Boris Brezillon <boris.brezillon at bootlin.com> wrote on Tue, 7 Aug 2018
> > 15:28:02 +0200:  
> > >> On Tue,  7 Aug 2018 14:16:52 +0200  
> >> Stefan Roese <sr at denx.de> wrote:
> >>  
> >>> Some SPI controller do not support full-duplex SPI transfers. This patch
> >>> changes the SPI transfer into 2 separate transfers - or 1, if no data is
> >>> to transmitted.
> >>>
> >>> With this change, no buffers need to be allocated anymore. We use the
> >>> TX and RX buffers that are passed to spi_mem_exec_op() directly.
> >>>
> >>> Signed-off-by: Stefan Roese <sr at denx.de>
> >>> Suggested-by: Boris Brezillon <boris.brezillon at bootlin.com>
> >>> Cc: Miquel Raynal <miquel.raynal at bootlin.com>
> >>> Cc: Boris Brezillon <boris.brezillon at bootlin.com>
> >>> Cc: Jagan Teki <jagan at openedev.com>  
> >>
> >> Looks good overall, just a few comments (that you might chose to ignore
> >> if you disagree).
> >>
> >> Reviewed-by: Boris Brezillon <boris.brezillon at bootlin.com>
> >>
> > > Sorry for being a bit late on the discussion, but while I do agree with  
> > the change, I'm not sure about its implementation : I think SPI
> > controllers are supposed to be abstracted by the SPI layer.
> > Addressing the controller's limitations in the SPI-mem layer would
> > not be appropriate.  
> > > Would it be possible to adapt spi_xfer() to handle such case?  
> 
> No, I don't think so. Its impossible to guess in the SPI driver layer,
> which parts of the message are TX data and which are RX data. So this
> message can't be split up into a half-duplex one here. This can only
> be done in the driver which constructs the SPI messages.
> 
> Or did I miss something here?

Actually I'm fine with it as SPI-mem only uses half-duplex. It's not
necessary to limit its use to SPI controllers (drivers) supporting
full-duplex.

Stefan, shall I fold your changes in my series and resend? Or do I
resend only my original patches and Jagan/Tom will apply yours on top
of it?

Thanks,
Miquèl