Re: [PATCH v5 2/3] memory: omap-gpmc: add support for wait pin polarity

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Hi Krzysztof,

On Mon, 2022-09-19 at 11:38 +0200, Krzysztof Kozlowski wrote:
> On 16/09/2022 14:07, B. Niedermayr wrote:
> > From: Benedikt Niedermayr <benedikt.niedermayr@xxxxxxxxxxx>
> > 
> > The waitpin polarity can be configured via the WAITPIN<X>POLARITY bits
> > in the GPMC_CONFIG register. This is currently not supported by the
> > driver. This patch adds support for setting the required register bits
> > with the "gpmc,wait-pin-polarity" dt-property.
> > 
> > Signed-off-by: Benedikt Niedermayr <benedikt.niedermayr@xxxxxxxxxxx>
> > ---
> >  drivers/memory/omap-gpmc.c              | 27 +++++++++++++++++++++++++
> >  include/linux/platform_data/gpmc-omap.h |  6 ++++++
> >  2 files changed, 33 insertions(+)
> > 
> > diff --git a/drivers/memory/omap-gpmc.c b/drivers/memory/omap-gpmc.c
> > index ea495e93766b..2853fc28bccc 100644
> > --- a/drivers/memory/omap-gpmc.c
> > +++ b/drivers/memory/omap-gpmc.c
> > @@ -132,6 +132,7 @@
> >  #define GPMC_CONFIG_DEV_SIZE	0x00000002
> >  #define GPMC_CONFIG_DEV_TYPE	0x00000003
> >  
> > +#define GPMC_CONFIG_WAITPINPOLARITY(pin)	(BIT(pin) << 8)
> >  #define GPMC_CONFIG1_WRAPBURST_SUPP     (1 << 31)
> >  #define GPMC_CONFIG1_READMULTIPLE_SUPP  (1 << 30)
> >  #define GPMC_CONFIG1_READTYPE_ASYNC     (0 << 29)
> > @@ -1882,6 +1883,17 @@ int gpmc_cs_program_settings(int cs, struct gpmc_settings *p)
> >  
> >  	gpmc_cs_write_reg(cs, GPMC_CS_CONFIG1, config1);
> >  
> > +	if (p->wait_pin_polarity != WAITPINPOLARITY_DEFAULT) {
> > +		config1 = gpmc_read_reg(GPMC_CONFIG);
> > +
> > +		if (p->wait_pin_polarity == WAITPINPOLARITY_ACTIVE_LOW)
> > +			config1 &= ~GPMC_CONFIG_WAITPINPOLARITY(p->wait_pin);
> > +		else if (p->wait_pin_polarity == WAITPINPOLARITY_ACTIVE_HIGH)
> > +			config1 |= GPMC_CONFIG_WAITPINPOLARITY(p->wait_pin);
> > +
> > +		gpmc_write_reg(GPMC_CONFIG, config1);
> 
> What happens if wait pin is shared and you have different polarities in
> both of devices?
In this case the second one wins and will overwrite the polarity of the first one.
But that would be the result of a misconfiguration in the DT. 

I'm not sure how to proceed here? Does it make sense to add a check for different 
waitpin polarities?


> 
> > +	}
> > +
> >  	return 0;
> >  }
> >  
> > @@ -1981,7 +1993,22 @@ void gpmc_read_settings_dt(struct device_node *np, struct gpmc_settings *p)
> >  				__func__);
> >  	}
> >  
> > +	p->wait_pin_polarity = WAITPINPOLARITY_DEFAULT;
> > +
> >  	if (!of_property_read_u32(np, "gpmc,wait-pin", &p->wait_pin)) {
> > +		if (!of_property_read_u32(np, "gpmc,wait-pin-polarity",
> > +					  &p->wait_pin_polarity)) {
> > +			if (p->wait_pin_polarity != WAITPINPOLARITY_ACTIVE_HIGH &&
> > +			    p->wait_pin_polarity != WAITPINPOLARITY_ACTIVE_LOW &&
> > +			    p->wait_pin_polarity != WAITPINPOLARITY_DEFAULT) {
> 
> WAITPINPOLARITY_DEFAULT is not allowed in DT, so you can skip it.
This value is not assigned from the DT. It is only assigned within the GPMC and serves as a init
value (right before the if clause). This helps in case no configuration from DT is done where the 
GPMC registers should stay untouched.

> 
> > +				pr_err("%s: Invalid wait-pin-polarity (pin: %d, pol: %d)\n",
> 
> dev_err, not pr_err

Ok. I didn't want to introduce dev_* functions. Currently pr_* functions where used all over the place.

> 
> > +				       __func__, p->wait_pin, p->wait_pin_polarity);
> 
> Skip __func__
> 
Ok.

> > +				p->wait_pin_polarity = WAITPINPOLARITY_DEFAULT;
> > +			}
> > +		} else {
> > +			pr_err("%s: Failed to read gpmc,wait-pin-polarity\n", __func__);
> 
> Ditto.
Ok.

> 
> > +		}
> > +
> >  		p->wait_on_read = of_property_read_bool(np,
> >  							"gpmc,wait-on-read");
> >  		p->wait_on_write = of_property_read_bool(np,
> > diff --git a/include/linux/platform_data/gpmc-omap.h b/include/linux/platform_data/gpmc-omap.h
> > index c9cc4e32435d..c46c28069c31 100644
> > --- a/include/linux/platform_data/gpmc-omap.h
> > +++ b/include/linux/platform_data/gpmc-omap.h
> > @@ -136,6 +136,11 @@ struct gpmc_device_timings {
> >  #define GPMC_MUX_AAD			1	/* Addr-Addr-Data multiplex */
> >  #define GPMC_MUX_AD			2	/* Addr-Data multiplex */
> >  
> > +/* Wait pin polarity values */
> > +#define WAITPINPOLARITY_DEFAULT -1
> 
> Missing prefix. This is a global header.
Ok. Makes sense.
> 
> > +#define WAITPINPOLARITY_ACTIVE_LOW 0
> > +#define WAITPINPOLARITY_ACTIVE_HIGH 1
> > +
> >  struct gpmc_settings {
> >  	bool burst_wrap;	/* enables wrap bursting */
> >  	bool burst_read;	/* enables read page/burst mode */
> > @@ -149,6 +154,7 @@ struct gpmc_settings {
> >  	u32 device_width;	/* device bus width (8 or 16 bit) */
> >  	u32 mux_add_data;	/* multiplex address & data */
> >  	u32 wait_pin;		/* wait-pin to be used */
> > +	u32 wait_pin_polarity;	/* wait-pin polarity */
> 
> Skip the comment. You just copied the name of variable. Such comments
> are useless.
> 
> We do not have KPIs in kernel to achieve some comment-ratio...
> 
Ok, makes sense.

> Best regards,
> Krzysztof





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