Re: nand-disk LED trigger: to remove, or not to remove

[Brian Norris <computersforpeace@gmail.com>]

On Tue, Apr 05, 2016 at 04:51:20PM -0300, Ezequiel Garcia wrote:
> Due to the way the 'nand-disk' LED trigger is implemented,
> it currently does not work correctly for all NAND drivers.
> 
> This is somewhat related to an old thread, where we discussed
> the addition of an "mtd" LED trigger. See:
> 
>   http://www.spinics.net/lists/linux-leds/msg01181.html
> 
> My question is:
> 
>  * given that nobody has complained about "nand-disk"
>    working on just some NAND drivers, and...
>  * given that nobody has complained (except that 2013 patch)
>    about lacking a generic MTD LED trigger...
> 
> Does it make any sense to have such a trigger at all?
> In other words, should we simply get rid of "nand-disk" trigger?

I don't have much opinion about the LED trigger, except that it'd be
nice if it either worked consistently or was removed.

> In case the answer is "We want to keep some LED trigger",
> then here's a patch for you to f̶l̶a̶m̶e̶  review:
> 
> From 88c7102bb67056b443da323bd3e28b60aca948a2 Mon Sep 17 00:00:00 2001
> From: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
> Date: Sat, 2 Apr 2016 18:35:50 -0300
> Subject: [PATCH] leds: trigger: Introduce a MTD (NAND/NOR) trigger
> 
> This commit introduces a MTD trigger for flash (NAND/NOR) device
> activity. The implementation is copied from IDE disk.
> 
> This deprecates the "nand-disk" LED trigger, but for backwards
> compatibility, we still keep the "nand-disk" trigger around.
> 
> The motivation for deprecating the "nand-disk" LED trigger is that
> it only works for NAND drivers, whereas the "mtd" LED trigger
> is more generic (in fact, "nand-disk" currently only works for
> certain NAND drivers).
> 
>   TODO: Measure how the trigger affects MTD I/O performance.
>   It should be cheap because the blink is deferred, but still
>   it makes sense to provide some hard numbers.
> 
> Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>

[...]

Notably, your patch changes the behavior pretty significantly. Instead
of triggering for individual NAND wait periods (very fine-grained) you
only trigger for entire write/read/erase operations. That may be OK,
especially if it's modelled after IDE.

I'd also note that you missed a few APIs (e.g., mtd_{read,write}_oob()).

Brian