Re: [PATCH v5 03/14] coresight: cti: Add sysfs access to program function regs

Mike Leach
2019-11-29T12:47:38Z

Hi Suzuki,

On Wed, 27 Nov 2019 at 18:26, Suzuki Kuruppassery Poulose
<suzuki.poulose@arm.com> wrote:
>
> On 19/11/2019 23:19, Mike Leach wrote:
> > Adds in sysfs programming support for the CTI function register sets.
> > Allows direct manipulation of channel / trigger association registers.
> >
> > Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> > Signed-off-by: Mike Leach <mike.leach@linaro.org>
> > ---
> > .../hwtracing/coresight/coresight-cti-sysfs.c | 362 ++++++++++++++++++
> > drivers/hwtracing/coresight/coresight-cti.c | 19 +
> > drivers/hwtracing/coresight/coresight-cti.h | 5 +
> > 3 files changed, 386 insertions(+)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-cti-sysfs.c b/drivers/hwtracing/coresight/coresight-cti-sysfs.c
> > index 507f8eb487fe..02d3ee0c1278 100644
> > --- a/drivers/hwtracing/coresight/coresight-cti-sysfs.c
> > +++ b/drivers/hwtracing/coresight/coresight-cti-sysfs.c
> > @@ -109,6 +109,362 @@ static struct attribute *coresight_cti_mgmt_attrs[] = {
> > NULL,
> > };
> >
> > +/* CTI low level programming registers */
> > +
> > +/*
> > + * Show a simple 32 bit value if enabled and powered.
> > + * If inaccessible & pcached_val not NULL then show cached value.
> > + */
>
> Also I am not sure if it makes sense to mention that the value is cached.
>
> > +static ssize_t cti_reg32_show(struct device *dev, char *buf,
> > + u32 *pcached_val, int reg_offset)
> > +{
> > + u32 val = 0;
> + char *state = "";
>
> > + struct cti_drvdata *drvdata = dev_get_drvdata(dev->parent);
> > + struct cti_config *config = &drvdata->config;
> > +
> > + spin_lock(&drvdata->spinlock);
> > + if ((reg_offset >= 0) && CTI_PWR_ENA(config)) {
>
> minor nit: Personally I don't like the naming here. This could simply
> be: cti_accessible(config) , may be defined as a static inline function
> instead of a macro:
>
> static inline bool cti_accessible(struct cti_drvdata *drvdata)
> {
> struct cti_config *cfg = &drvdata->config;
>
> return cfg->hw_powered && cfg->hw_enabled;
> }
>
>

Since this is a generic access function used throughout the file - the
cached pointer is an indicator used by the callee that there is a
value available if the CTI is unpowered / disabled - so the function
can show an appropriate value which will be taken from the config
structure.

So I don't think it is relevant to show that a "cached" value is being
used to show the user. If you look at similar functions in the ETM
drivers for example, quite often a show function simple shows that
stored value from a config structure without ever looking at the
register in the device.

As to naming - the name is chosen to represent a specific state - both
powered and enabled. The sysfs interface is accessible in any state -
powered / unpowered , enabled /disabled - so I am being specific.
Unlike the ETM, this hardware can have registers programmed while
enabled - and for some such as apppulse this is the only time it makes
sense to use them.

I don't mind either way between macro / inline function - though it
still has to be declared in the header as it is used in multiple .c
files.
I'd be inclined to call it cti_active() if preferred to cti_pwr_ena -
active implies that the CTI is in operation.

Thanks

Mike

> > + CS_UNLOCK(drvdata->base);
> > + val = readl_relaxed(drvdata->base + reg_offset);
> > + if (pcached_val)
> > + *pcached_val = val;
> > + CS_LOCK(drvdata->base);
> > + } else if (pcached_val) {
> > + val = *pcached_val;
>
> + state = " (cached)";
> > + }
> > + spin_unlock(&drvdata->spinlock);
> > + return scnprintf(buf, PAGE_SIZE, "%#x\n", val);
> + return scnprintf(buf, PAGE_SIZE, "%#x%s\n", val, state);
>
> > +}
> > +
> > +/*
> > + * Store a simple 32 bit value.
> > + * If pcached_val not NULL, then copy to here too,
> > + * if reg_offset >= 0 then write through if enabled.
> > + */
> > +static ssize_t cti_reg32_store(struct device *dev, const char *buf,
> > + size_t size, u32 *pcached_val, int reg_offset)
>
>
> > +static ssize_t appclear_store(struct device *dev,
> > + struct device_attribute *attr,
> > + const char *buf, size_t size)
> > +{
> > + unsigned long val;
> > + struct cti_drvdata *drvdata = dev_get_drvdata(dev->parent);
> > + struct cti_config *config = &drvdata->config;
> > +
> > + if (kstrtoul(buf, 0, &val))
> > + return -EINVAL;
> > +
> > + spin_lock(&drvdata->spinlock);
> > +
> > + /* a 1'b1 in appclr clears down the same bit in appset*/
>
> nit: a 0b1 ?
>
Syntax is <bitwidth>'<radix><value> - a habit picked up from verilog.

> > + config->ctiappset &= ~val;
> > +
> > + /* write through if enabled */
> > + if (CTI_PWR_ENA(config))
> > + cti_write_single_reg(drvdata, CTIAPPCLEAR, val);
> > + spin_unlock(&drvdata->spinlock);
> > + return size;
> > +}
> > +static DEVICE_ATTR_WO(appclear);
> > +
>
> Otherwise looks good to me.
>
> Suzuki

--
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK