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

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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) {




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