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

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Stefan, Jagan,

Boris Brezillon <boris.brezillon@bootlin.com> wrote on Tue, 7 Aug 2018
15:28:02 +0200:

> On Tue,  7 Aug 2018 14:16:52 +0200
> Stefan Roese <sr@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@denx.de>
> > Suggested-by: Boris Brezillon <boris.brezillon@bootlin.com>
> > Cc: Miquel Raynal <miquel.raynal@bootlin.com>
> > Cc: Boris Brezillon <boris.brezillon@bootlin.com>
> > Cc: Jagan Teki <jagan@openedev.com>  
> 
> Looks good overall, just a few comments (that you might chose to ignore
> if you disagree).
> 
> Reviewed-by: Boris Brezillon <boris.brezillon@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? 

Thanks,
Miquèl