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

[Stefan Roese]

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.

Thanks,
Stefan