Re: [PATCH v2] Add support for PCIe SSD status LED management

From: "Marek Behún" <marek.behun@nic.cz>
To: stuart hayes <stuart.w.hayes@gmail.com>
Cc: Pavel Machek <pavel@ucw.cz>, Randy Dunlap <rdunlap@infradead.org>,
	Bjorn Helgaas <bhelgaas@google.com>,
	linux-pci@vger.kernel.org, Keith Busch <kbusch@kernel.org>,
	kw@linux.com,
	"linux-leds@vger.kernel.org" <linux-leds@vger.kernel.org>
Subject: Re: [PATCH v2] Add support for PCIe SSD status LED management
Date: Wed, 2 Jun 2021 18:33:28 +0200	[thread overview]
Message-ID: <20210602183328.1e5885dc@dellmb> (raw)
In-Reply-To: <6ee11975-fad7-1a82-f7f3-279ebd4f67cb@gmail.com>

On Tue, 1 Jun 2021 22:18:16 -0500
stuart hayes <stuart.w.hayes@gmail.com> wrote:

> Both Bjorn Helgaas and Krzysztof Wilczyński had suggested the 
> scheduler-type interface, so I went with that.  In an earlier attempt
> at this driver, when Bjorn suggested this, he asked if that would
> violate the "one value per file" rule, and Greg K-H responded "That's
> a valid way of displaying options for a sysfs file that can be
> specific unique values."

But you are not displaying unique values. Your example is

# echo "ok locate" >/sys/class/leds/0000:88:00.0::drive_status/states
# cat /sys/class/leds/0000:88:00.0::drive_status/states
[ok] [locate] failed rebuild pfa hotspare ica ifa invalid disabled

so there are 2 values set (ok and locate). Unique means that only one
can be set.

Question: can this LED be configured by userspace? I mean: can you
configure whether the LED should be on/off, disregarding the SSD state?

I ask because the LED subsystem currently officially does not
support LEDs for which brightness cannot be set by userspace...

If yes, you should implement the .brightness_set() function. (Could you
please also send your patch to the linux-leds mailing list?)

Then you should implement a LED-private trigger for this LED, which,
when enabled, will make the LED follow the SSD state.

The sysfs ABI should probably look like this:

# cd /sys/class/leds/<SSD_LED>
# echo 1 >brightness		# to light the LED on
# echo 0 >brightness		# to light the LED off
# echo ssd_state >trigger	# to make the LED follow SSD states
# ls ssd_state			# list available SSD states
ok  locate  failed  rebuild ...
# cat ssd_state/ok		# check if "ok" state is enabled
0
# echo 1 >ssd_state/ok		# enable "ok" state so that the
				# LED will be on when SSD is in "ok"
				# state
# echo none >trigger		# put the LED back into SW mode

(The name of the trigger does not necessarily have to be "ssd_state".
 Other people should give their opinions about the name.)

Marek