[U-Boot] [PATCH] spi: cadence_qspi: Ensure spi_calibration is run when sclk change

[Chin Liang See]

On Tue, 2015-09-01 at 11:19 +0200, marex at denx.de wrote:
> On Tuesday, September 01, 2015 at 11:13:38 AM, Chin Liang See wrote:
> > On Tue, 2015-09-01 at 11:01 +0200, marex at denx.de wrote:
> > > On Tuesday, September 01, 2015 at 10:46:47 AM, Chin Liang See wrote:
> > > > Ensuring spi_calibration is run when there is a change of sclk
> > > > frequency. This will ensure the qspi flash access works for high
> > > > sclk frequency
> > > > 
> > > > Signed-off-by: Chin Liang See <clsee at altera.com>
> > > > Cc: Dinh Nguyen <dinguyen at opensource.altera.com>
> > > > Cc: Marek Vasut <marex at denx.de>
> > > > Cc: Stefan Roese <sr at denx.de>
> > > > Cc: Vikas Manocha <vikas.manocha at st.com>
> > > > Cc: Jagannadh Teki <jteki at openedev.com>
> > > > Cc: Pavel Machek <pavel at denx.de>
> > > > ---
> > > > 
> > > >  drivers/spi/cadence_qspi.c |    3 +++
> > > >  1 files changed, 3 insertions(+), 0 deletions(-)
> > > > 
> > > > diff --git a/drivers/spi/cadence_qspi.c b/drivers/spi/cadence_qspi.c
> > > > index 34a0f46..512bf2d 100644
> > > > --- a/drivers/spi/cadence_qspi.c
> > > > +++ b/drivers/spi/cadence_qspi.c
> > > > @@ -128,6 +128,9 @@ static int cadence_spi_set_speed(struct udevice
> > > > *bus, uint hz)
> > > > 
> > > >  	cadence_spi_write_speed(bus, hz);
> > > > 
> > > > +	/* to ensure spi_calibration is run when SCLK frequency change */
> > > > +	plat->max_hz = hz;
> > > > +
> > > 
> > > This looks like a hack, doesn't this change just subvert the condition
> > > below to enforce the calibration ?
> > 
> > Nope. I checked through debugger where plat->max_hz is initialized once
> > with the value from device tree. When you use sf probe to change
> > frequency, the value is not reflected to plat->max_hz. Hence the
> > calibration is not run when frequency change. That lead to the sf probe
> > fail when running at 80MHz or higher. Note the priv->qspi_calibrated_hz
> > is updated after calibration succeed.
> 
> Isn't the purpose of ->max_hz to reflect the maximum frequency of the bus?
> I don't think this should thus ever be updated, in particular not by the
> user. I also think that setting ->max_hz once from DT is the correct behavior.
> 

Oh, in this case, there are more bug in the code. I saw there is
mismatch of the usage of this variable. As example, the line
"priv->qspi_calibrated_hz = plat->max_hz;" is wrong as it would be
always static. Besides that, there is no check against the requested
speed not to exceed the max_hz. Let me fix this all again.

Thanks
Chin Liang

> Best regards,
> Marek Vasut