Re: [PATCHv3 1/2] spi: imx: fix use of native chip-selects with devicetree

[Oleksij Rempel <ore@xxxxxxxxxxxxxx>]

On Thu, Jul 20, 2017 at 11:00:49PM +1000, Greg Ungerer wrote:
> Hi Oleksij,
> 
> On 20/07/17 16:34, Oleksij Rempel wrote:
> > Hi Greg,
> > 
> > On Tue, Jul 18, 2017 at 09:53:58PM -0300, Fabio Estevam wrote:
> > > Adding Pengutronix folks on Cc.
> > > 
> > > On Tue, Jul 11, 2017 at 1:22 AM, Greg Ungerer <gerg@xxxxxxxxxxxxxx> wrote:
> > > > The commonly used mechanism of specifying the hardware or native
> > > > chip-select on an SPI device in devicetree (that is "cs-gpios = <0>")
> > > > does not result in the native chip-select being configured for use.
> > > > So external SPI devices that require use of the native chip-select
> > > > will not work.
> > > > 
> > > > You can successfully specify native chip-selects if using a platform
> > > > setup by specifying the cs-gpio as negative offset by 32. And that
> > > > works correctly. You cannot use the same method in devicetree.
> > > > 
> > > > The logic in the spi-imx.c driver during probe uses core spi function
> > > > of_spi_register_master() in spi.c to parse the "cs-gpios" devicetree tag.
> > > > For valid GPIO values that will be recorded for use, all other entries in
> > > > the cs_gpios list will be set to -ENOENT. So entries like "<0>" will be
> > > > set to -ENOENT in the cs_gpios list.
> > > > 
> > > > When the SPI device registers are setup the code will use the GPIO
> > > > listed in the cs_gpios list for the desired chip-select. If the cs_gpio
> > > > is less then 0 then it is intended to be for a native chip-select, and
> > > > its cs_gpio value is added to 32 to get the chipselect number to use.
> > > > Problem is that with devicetree this can only ever be -ENOENT (which
> > > > is -2), and that alone results in an invalid chip-select number. But also
> > > > doesn't allow selection of the native chip-select at all.
> > > > 
> > > > To fix, if the cs_gpio specified for this spi device is not a
> > > > valid GPIO then use the "chip_select" (that is the native chip-select
> > > > number) for hardware setup.
> > > > 
> > > > Signed-off-by: Greg Ungerer <gerg@xxxxxxxxxxxxxx>
> > > > ---
> > > >   drivers/spi/spi-imx.c | 8 ++++----
> > > >   1 file changed, 4 insertions(+), 4 deletions(-)
> > > > 
> > > > diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
> > > > index b402530..f4fe66c 100644
> > > > --- a/drivers/spi/spi-imx.c
> > > > +++ b/drivers/spi/spi-imx.c
> > > > @@ -524,8 +524,8 @@ static int mx31_config(struct spi_device *spi, struct spi_imx_config *config)
> > > >                  reg |= MX31_CSPICTRL_POL;
> > > >          if (spi->mode & SPI_CS_HIGH)
> > > >                  reg |= MX31_CSPICTRL_SSPOL;
> > > > -       if (spi->cs_gpio < 0)
> > > > -               reg |= (spi->cs_gpio + 32) <<
> > > > +       if (!gpio_is_valid(spi->cs_gpio))
> > > > +               reg |= (spi->chip_select) <<
> > > >                          (is_imx35_cspi(spi_imx) ? MX35_CSPICTRL_CS_SHIFT :
> > > >                                                    MX31_CSPICTRL_CS_SHIFT);
> > > > 
> > > > @@ -616,8 +616,8 @@ static int mx21_config(struct spi_device *spi, struct spi_imx_config *config)
> > > >                  reg |= MX21_CSPICTRL_POL;
> > > >          if (spi->mode & SPI_CS_HIGH)
> > > >                  reg |= MX21_CSPICTRL_SSPOL;
> > > > -       if (spi->cs_gpio < 0)
> > > > -               reg |= (spi->cs_gpio + 32) << MX21_CSPICTRL_CS_SHIFT;
> > > > +       if (!gpio_is_valid(spi->cs_gpio))
> > > > +               reg |= spi->chip_select << MX21_CSPICTRL_CS_SHIFT;
> > > > 
> > > >          writel(reg, spi_imx->base + MXC_CSPICTRL);
> > > > 
> > 
> > hm... do I see this correctly, all native chip_selects should
> > be registered before gpio based CS?
> 
> I don't follow. The "<0>" must be in the position in the list where
> you want to use the native chip select. You can't arbitrarily change
> the order.
> 
> 
> > For example like this?
> > cs-gpios = <0>, <&gpio1 1 0>, <&gpio1 2 0>;
> > 
> > Looks like we don't have any sanity checks for this kind of
> > configuration:
> > cs-gpios = <&gpio1 1 0>, <&gpio1 2 0>, <0>;
> 
> The chip_select is sanity checked in spi_add_device().
> 
> 
> > We may shift some wired numbers here:
> > reg |= spi->chip_select << MX21_CSPICTRL_CS_SHIFT;
> 
> I am not sure I see how that can be the case?

old and new version of iMX have different amount of native CS.
I can't find the code which is actually checking if we use right native
CS-index.
May be i'm blind :)

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