[PATCH 1/1] Fix wrong QSPI clock calculation for AM4372

[Stefan Mätje]

Am Montag, den 29.11.2021, 22:58 -0500 schrieb Tom Rini:
> On Tue, Nov 30, 2021 at 01:06:56AM +0100, Stefan Mätje wrote:
> 
> > On AM4372 the SPI_GCLK input gets its clock from the PRCM module which
> > divides the PER_CLKOUTM2 frequency (192MHz) by a fixed factor of 4.
> > See AM437x Reference Manual in section 27 QSPI >> 27.2 Integration.
> > 
> > The QSPI_FCLK therefore needs to take this factor into account and
> > becomes (192000000 / 4).
> > 
> > Signed-off-by: Stefan Mätje <stefan.maetje at esd.eu>
> > ---
> >  drivers/spi/ti_qspi.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/spi/ti_qspi.c b/drivers/spi/ti_qspi.c
> > index 664b9cad79..bccdeeaf82 100644
> > --- a/drivers/spi/ti_qspi.c
> > +++ b/drivers/spi/ti_qspi.c
> > @@ -25,7 +25,8 @@ DECLARE_GLOBAL_DATA_PTR;
> >  
> >  /* ti qpsi register bit masks */
> >  #define QSPI_TIMEOUT                    2000000
> > -#define QSPI_FCLK			192000000
> > +/* AM4372: QSPI gets SPI_GCLK from PRCM unit as PER_CLKOUTM2 divided by 4.
> > */
> > +#define QSPI_FCLK                       (192000000 / 4)
> >  #define QSPI_DRA7XX_FCLK                76800000
> >  #define QSPI_WLEN_MAX_BITS		128
> >  #define QSPI_WLEN_MAX_BYTES		(QSPI_WLEN_MAX_BITS >> 3)
> 
> How is this treated in the kernel?  Thanks.
> 
The current driver in mainline Linux  @drivers/spi/spi-ti-qspi.c still has
the wrong QSPI_FCLK define, but it seems to be used nowhere any more.

The driver gets its "fclk" from the device tree. But the device tree
(arch/arm/boot/dts/am4372.dtsi) was broken till this patch on the
mainline kernel:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/arm/boot/dts/am4372.dtsi?id=f60c41257fa06d496c9653d3f77d34b7426d9274

It seems to me that there the first time a valid "fclk" property
was provided to the qspi module.

Best regards,
    Stefan Mätje