Re: [PATCH -next 3/4] spi: mockup: Add runtime device tree overlay interface

[weiyongjun (A)]

On 2022/8/30 5:29, Frank Rowand wrote:
> comment inline below, plus adding to cc: and to: list
>
> On 8/26/22 09:43, Wei Yongjun wrote:
> > Add a runtime device tree overlay interface for device need dts file.
> > With it its possible to use device tree overlays without having to use
> > a per-platform overlay manager.
>
> Why is an overlay needed?  The documentation in patch 4 shows providing
> a dtb as an argument to the qemu-system-x86_64 command, which should be
> sufficient to supply the appropriate dtb.

Fist, we are aimed to build a device driver regression testsuit. Without
overlay, lots of the dtb fragments must be combined to a very big one, it
may different to maintainence. overlay makes easily to attach/detech as
the device's requirement.

Seconds, overlay dts may be used to found or verification issues related
to of_node_put or others, such as patches like:

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/?qt=grep&q=node_put

many of them may found by static check tool, which may leak of tesing.

The documentation I post does not use overlay dts, but when overlay
dts[1] is used, we can found the of node leak:

$ python3 -m kddv.cmds.mock -b spi -d mchp23k256
create spi device mchp23k256 success!
$ ls /sys/bus/spi/drivers/mchp23k256/spi0.0/mtd/
mtd0  mtd0ro
$ python3 -m kddv.cmds.mock -b spi -d mchp23k256 -r
[  233.508565] Deleting MTD partitions on "spi0.0":
[  233.516784] OF: ERROR: memory leak, expected refcount 1 instead of 2,
 of_node_get()/of_node_put() unbalanced - destroy cset entry: attach
 overlay node /spi/spi-sram@0
remove spi device mchp23k256 success!

Not sure it is worth to fix issues like this, but at least, we can
tesing them now.

-[1]---------------------------------------------------------
/dts-v1/;
/plugin/;

&{/spi} {
	spi-sram@0 {
		#address-cells = <1>;
		#size-cells = <1>;
		compatible = "microchip,mchp23k256";
		reg = <0>;
		spi-max-frequency = <20000000>;
	};
};

-------------------------------------------------------

Regards,
Wei Yongjun

> -Frank
>
> > Add a new device by command:
> > $ cat test.dtbo > /sys/class/spi_master/spi0/overlay_fdto
> >
> > Remove the device by command:
> > $ echo remove > /sys/class/spi_master/spi0/overlay_fdto
> >
> > Signed-off-by: Wei Yongjun <weiyongjun1@xxxxxxxxxx>
> > ---
> >   drivers/spi/Kconfig      |  2 ++
> >   drivers/spi/spi-mockup.c | 48 ++++++++++++++++++++++++++++++++++++++++
> >   2 files changed, 50 insertions(+)
> >
> > diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
> > index e0f0fa2746ad..4b7c84ddb367 100644
> > --- a/drivers/spi/Kconfig
> > +++ b/drivers/spi/Kconfig
> > @@ -1161,6 +1161,8 @@ config SPI_TLE62X0
> >   config SPI_MOCKUP
> >   	tristate "SPI controller Testing Driver"
> >   	depends on OF
> > +	select OF_EARLY_FLATTREE
> > +	select OF_RESOLVE
> >   	select BPF_EVENTS
> >   	help
> >   	  This enables SPI controller testing driver, which provides a way to
> > diff --git a/drivers/spi/spi-mockup.c b/drivers/spi/spi-mockup.c
> > index 7a93b194ee53..404ad821bf6a 100644
> > --- a/drivers/spi/spi-mockup.c
> > +++ b/drivers/spi/spi-mockup.c
> > @@ -21,6 +21,9 @@
> >   struct mockup_spi {
> >   	struct mutex lock;
> >   	struct spi_device *devs[MOCKUP_CHIPSELECT_MAX];
> > +
> > +	void *fdto;
> > +	int ovcs_id;
> >   };
> >   
> >   static struct spi_master *to_spi_master(struct device *dev)
> > @@ -145,9 +148,53 @@ delete_device_store(struct device *dev, struct device_attribute *attr,
> >   }
> >   static DEVICE_ATTR_WO(delete_device);
> >   
> > +static ssize_t
> > +overlay_fdto_store(struct device *dev, struct device_attribute *attr,
> > +		   const char *buf, size_t count)
> > +{
> > +	struct spi_master *master = to_spi_master(dev);
> > +	struct mockup_spi *mock = spi_master_get_devdata(master);
> > +	int ret;
> > +
> > +	mutex_lock(&mock->lock);
> > +
> > +	if (strncmp(buf, "remove\n", count) == 0) {
> > +		if (mock->ovcs_id < 0) {
> > +			ret = -ENOENT;
> > +			goto out_unlock;
> > +		}
> > +		of_overlay_remove(&mock->ovcs_id);
> > +		kfree(mock->fdto);
> > +		mock->ovcs_id = -1;
> > +		mock->fdto = NULL;
> > +	} else {
> > +		if (mock->ovcs_id >= 0) {
> > +			ret = -EINVAL;
> > +			goto out_unlock;
> > +		}
> > +		mock->fdto = kmemdup(buf, count, GFP_KERNEL);
> > +		if (!mock->fdto) {
> > +			ret = -ENOMEM;
> > +			goto out_unlock;
> > +		}
> > +		ret = of_overlay_fdt_apply(mock->fdto, count, &mock->ovcs_id);
> > +		if (ret < 0)
> > +			goto out_unlock;
> > +	}
> > +
> > +	mutex_unlock(&mock->lock);
> > +	return count;
> > +
> > +out_unlock:
> > +	mutex_unlock(&mock->lock);
> > +	return ret;
> > +}
> > +static DEVICE_ATTR_WO(overlay_fdto);
> > +
> >   static struct attribute *spi_mockup_attrs[] = {
> >   	&dev_attr_new_device.attr,
> >   	&dev_attr_delete_device.attr,
> > +	&dev_attr_overlay_fdto.attr,
> >   	NULL
> >   };
> >   ATTRIBUTE_GROUPS(spi_mockup);
> > @@ -227,6 +274,7 @@ static int spi_mockup_probe(struct platform_device *pdev)
> >   
> >   	mock = spi_master_get_devdata(master);
> >   	mutex_init(&mock->lock);
> > +	mock->ovcs_id = -1;
> >   
> >   	ret = spi_register_master(master);
> >   	if (ret) {