Hi,
On Mon, Mar 23, 2020 at 02:36:23PM -0500, Pierre-Louis Bossart wrote:
Add attribute and show the components string. This is useful to see what is provided to userspace and e.g. used by UCM to understand the card configuration:
root@plb:~# more /sys/class/sound/card0/components HDA:8086280b,80860101,00100000 cfg-spk:2 hs:rt711 spk:rt1308 mic:rt715
Note that the style uses what's recommended by checkpatch.pl and is slightly different from other sysfs attributes.
Signed-off-by: Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com
sound/core/init.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
I have a concern about this patch in a point of userspace interface.
The 'component' field of 'struct snd_ctl_card_info' is just defined to have strings with space-separated chunks, and its actual value is not so fine-documented, thus it's largely different depending of developers of each driver.
$ cat include/uapi/sound/asound.h ... 941 struct snd_ctl_card_info { ... 950 unsigned char components[128]; /* card components / fine identification, delimited with one space (AC97 etc..) */ 951 };
On the other hand, the node of sysfs is quite common in Linux because it's tightly coupled to kernel objects. Let you see files under 'Documentation/ABI/'. We can find efforts to maintain sysfs node so safe and stable. Due to this reason, it's better to take more care when adding new node.
Would I request you the reason to add this node and the reason that current ALSA control interface doesn't satisfy your requirement?
diff --git a/sound/core/init.c b/sound/core/init.c index b02a99766351..decaf944a8ad 100644 --- a/sound/core/init.c +++ b/sound/core/init.c @@ -695,9 +695,21 @@ card_number_show_attr(struct device *dev,
static DEVICE_ATTR(number, 0444, card_number_show_attr, NULL);
+static ssize_t +components_show(struct device *dev,
struct device_attribute *attr, char *buf)+{
- struct snd_card *card = container_of(dev, struct snd_card, card_dev);
- return scnprintf(buf, PAGE_SIZE, "%s\n", card->components);
+}
+static DEVICE_ATTR_RO(components);
static struct attribute *card_dev_attrs[] = { &dev_attr_id.attr, &dev_attr_number.attr,
- &dev_attr_components.attr, NULL
};
-- 2.20.1
Regards
Takashi Sakamoto