LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Pavel Machek <pavel@ucw.cz>
To: Jacek Anaszewski <j.anaszewski@samsung.com>
Cc: Greg KH <greg@kroah.com>,
	kernel list <linux-kernel@vger.kernel.org>,
	linux-leds@vger.kernel.org, devicetree@vger.kernel.org,
	kyungmin.park@samsung.com, b.zolnierkie@samsung.com,
	cooloney@gmail.com, rpurdie@rpsys.net, sakari.ailus@iki.fi,
	s.nawrocki@samsung.com
Subject: Re: Reading /sys with side effects (was Re: [PATCH 1/2] Documentation: leds: Add description of LED Flash class extension)
Date: Mon, 2 Feb 2015 14:51:03 +0100	[thread overview]
Message-ID: <20150202135103.GB26985@amd> (raw)
In-Reply-To: <54CF65CB.3060207@samsung.com>

Hi!

> >[Actually, you could _always_ do two reads on those devices, discard
> >first result, and return the second. But I'm not sure how hardware
> >will like that.]
> 
> This would be the most sensible option.
> 
> 
> However, let's analyze the typical use cases for flash strobing:
> 
> 
> -------------------------------------------------------------
> 
> 
> >>>>>>>> Version without faults caching:
> 
> ============
> Driver side:
> ============
> 
> read_faults()
> 	faults = read_i2c(); //read faults
> 	if faults
> 		write_i2c(); //clear faults, only for some devices
> 		faults = read_i2c(); //read faults
> 	return faults
> 
> ================
> User space side:
> ================
> 
> 1. faults = `cat flash_faults` //read_faults()
> 2. if faults then
> 	print "Unable to strobe the flash LED due to faults"
>    else
> 	echo 1 > flash_strobe
> 
> 
> >>>>>>>> Version with faults caching:
> 
> ============
> Driver side:
> ============
> 
> read_faults()
> 	faults |= read_i2c(); //read faults
> 
> clear_faults()
> 	write_i2c(); //clear faults
> 	faults = 0;
> 
> 
> ================
> User space side:
> ================
> 
> 1. faults = `cat flash_faults` //read_faults()
> 2. if faults then
> 	echo 0 > flash_faults  //clear_faults()
> 	faults = `cat flash_faults` //read_faults()
> 3, if !faults
> 	echo 1 > flash_strobe
>    else
> 	print "Unable to strobe the flash LED due to faults"
> 
> 
> -------------------------------------------------------------
> 
> From the above it seems that version with clearing faults on read
> results in the simpler flash strobing procedure on userspace side,
> by the cost of additional bus access on the driver side.

I like caching version more (as it will allow by-hand debugging of
"why did not flash fire? Aha, lets see in the file, there was fault),
but both should be acceptable.

> we don't need additional attribute, just writing the flash_faults
> attribute can do the clearing.

Yes, writing flash_faults to clear is acceptable.
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

  reply	other threads:[~2015-02-02 13:51 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1422346028-16739-1-git-send-email-j.anaszewski@samsung.com>
2015-01-27 22:37 ` Pavel Machek
2015-01-28  8:43   ` Jacek Anaszewski
2015-01-29 21:14     ` Pavel Machek
2015-01-30  8:55       ` Jacek Anaszewski
2015-01-30 16:40         ` Greg KH
2015-02-02  9:07           ` Jacek Anaszewski
2015-02-02  9:44             ` Pavel Machek
2015-02-02 11:55               ` Jacek Anaszewski
2015-02-02 13:51                 ` Pavel Machek [this message]
2015-02-02 14:51                   ` Jacek Anaszewski

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20150202135103.GB26985@amd \
    --to=pavel@ucw.cz \
    --cc=b.zolnierkie@samsung.com \
    --cc=cooloney@gmail.com \
    --cc=devicetree@vger.kernel.org \
    --cc=greg@kroah.com \
    --cc=j.anaszewski@samsung.com \
    --cc=kyungmin.park@samsung.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-leds@vger.kernel.org \
    --cc=rpurdie@rpsys.net \
    --cc=s.nawrocki@samsung.com \
    --cc=sakari.ailus@iki.fi \
    --subject='Re: Reading /sys with side effects (was Re: [PATCH 1/2] Documentation: leds: Add description of LED Flash class extension)' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).