[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 11:10:15 +0200:

> Hi Miquel,
> 
> On 09.08.2018 10:13, Miquel Raynal wrote:
> > 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?  
> 
> Do you need to re-send your original patches? If yes, then please do
> with my patches folded in. If a re-send is not necessary, then Jagan
> or Tom should be able to apply your latest patchset and mine on top
> of it.

I suppose Jagan prefers formal patches than a Github branch so
basically I have to pull Boris fixes, squash them, do the same with
yours and resend.

As we missed the merge window, maybe I'll also take the time to rework
mtdparts. I plan to do that next week.

Thanks for your help,
Miquèl