[RFC PATCH 2/2] spi: Add support for Zynq Ultrascale+ MPSoC GQSPI controller

Mark Brown broonie at kernel.org
Thu May 28 08:03:56 PDT 2015

On Fri, May 22, 2015 at 08:43:54PM +0530, Harini Katakam wrote:
> On Fri, May 22, 2015 at 5:28 PM, Mark Brown <broonie at kernel.org> wrote:
> > On Wed, May 20, 2015 at 12:57:51PM +0530, Ranjit Waghmode wrote:

> > Why is there a default case here?  That's going to men we try to handle
> > any random chip select that gets passed in as pointing to this lower
> > device which doesn't seem right.  The fact that this is trying to handle
> > mirroring of the chip select to two devices is also raising alarm bells
> > here...

> This SPI controller has two CS lines and two data bus.
> Two devices can be connected to these and either the upper or the
> lower or both (Explained below) can be selected.

> When two flash devices are used, one of the HW configurations in
> which they can be connected is called "parallel" mode where they

I know what wiring chip selects in parallel is but that's not the
question - the question is about the handling of the default case.

> >> +static void zynqmp_qspi_chipselect(struct spi_device *qspi, bool is_high)
> >> +{

> >> +     if (is_high) {
> >> +             /* Manually start the generic FIFO command */
> >> +             zynqmp_gqspi_write(xqspi, GQSPI_CONFIG_OFST,
> >> +                             zynqmp_gqspi_read(xqspi, GQSPI_CONFIG_OFST) |
> >> +                             GQSPI_CFG_START_GEN_FIFO_MASK);

> > No, this is broken - setting the chip select should set the chip select,
> > it shouldn't have any impact on transfers.  Transfers should be started
> > in the transfer operations.

> This is the only way to assert the CS. It doesn't start transferring any data.

OK, then you can't implement a separate set_cs() operation and shouldn't
be trying to do so.  This will break in multiple ways when the framework
tries to use the operations separately.  You probably need to implement
a single flat transfer() operation.
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