Re: [PATCH v6 09/13] Add nodes for dsb edge control

[Greg Kroah-Hartman]

On Tue, Jun 20, 2023 at 04:31:59PM +0800, Tao Zhang wrote:
> 
> On 6/20/2023 3:37 PM, Greg Kroah-Hartman wrote:
> > On Tue, Jun 20, 2023 at 03:32:37PM +0800, Tao Zhang wrote:
> > > Add the nodes to set value for DSB edge control and DSB edge
> > > control mask. Each DSB subunit TPDM has maximum of n(n<16) EDCR
> > > resgisters to configure edge control. DSB edge detection control
> > > 00: Rising edge detection
> > > 01: Falling edge detection
> > > 10: Rising and falling edge detection (toggle detection)
> > > And each DSB subunit TPDM has maximum of m(m<8) ECDMR registers to
> > > configure mask. Eight 32 bit registers providing DSB interface
> > > edge detection mask control.
> > > 
> > > Signed-off-by: Tao Zhang <quic_taozha@xxxxxxxxxxx>
> > > ---
> > >   .../ABI/testing/sysfs-bus-coresight-devices-tpdm   |  32 +++++
> > >   drivers/hwtracing/coresight/coresight-tpdm.c       | 143 ++++++++++++++++++++-
> > >   drivers/hwtracing/coresight/coresight-tpdm.h       |  22 ++++
> > >   3 files changed, 196 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpdm b/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpdm
> > > index 2a82cd0..34189e4a 100644
> > > --- a/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpdm
> > > +++ b/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpdm
> > > @@ -60,3 +60,35 @@ Description:
> > >   		Bit[3] : Set to 0 for low performance mode.
> > >   				 Set to 1 for high performance mode.
> > >   		Bit[4:8] : Select byte lane for high performance mode.
> > > +
> > > +What:		/sys/bus/coresight/devices/<tpdm-name>/dsb_edge_ctrl
> > > +Date:		March 2023
> > > +KernelVersion	6.5
> > > +Contact:	Jinlong Mao (QUIC) <quic_jinlmao@xxxxxxxxxxx>, Tao Zhang (QUIC) <quic_taozha@xxxxxxxxxxx>
> > > +Description:
> > > +		Read/Write a set of the edge control registers of the DSB
> > > +		in TPDM.
> > > +
> > > +		Expected format is the following:
> > > +		<integer1> <integer2> <integer3>
> > sysfs is "one value", not 3.  Please never have to parse a sysfs file.
> 
> Do you mean sysfs file can only accept "one value"?

Yes.

> I see that more than one value are written to the sysfs file
> "trigout_attach".

Then someone missed that and it needs to be fixed.

> > > +static ssize_t dsb_edge_ctrl_show(struct device *dev,
> > > +				       struct device_attribute *attr,
> > > +				       char *buf)
> > > +{
> > > +	struct tpdm_drvdata *drvdata = dev_get_drvdata(dev->parent);
> > > +	ssize_t size = 0;
> > > +	unsigned long bytes;
> > > +	int i;
> > > +
> > > +	spin_lock(&drvdata->spinlock);
> > > +	for (i = 0; i < TPDM_DSB_MAX_EDCR; i++) {
> > > +		bytes = sysfs_emit_at(buf, size,
> > > +				  "Index:0x%x Val:0x%x\n", i,
> > Again, no, one value, no "string" needed to parse anything.
> 
> I also see other sysfs files can be read more than one value in other
> drivers.

Again, they are broken, please send patches to fix them.

> Is this "one value" limitation the usage rule of Linux sysfs system?

Yes.

thanks,

greg k-h