[Letux-kernel] [Kernel] Pyra: is31fl319x V2 driver (RGB-LEDs)

[H. Nikolaus Schaller]

> Am 24.06.2016 um 22:06 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> 
> 
>> Am 23.06.2016 um 18:48 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
>> 
>> Hi,
>> I did have this driver for a while on my to-do list time to finalise the feedbacks I got
>> for V1 from LKML.
>> 
>> The only unprocessed feedback was to use a regmap for optimizing the
>> i2c traffic and solving the issue that we must read back all LED brightness
>> values to determine if the chip can be shut down. But there is no i2c read
>> response for this chip. So regmap should cache the last value written.
>> 
>> With the lastest patch It - almost - works like with our own hacks of V1...
>> 
>> Only problem seems how to correctly setup the regmap so that it never
>> really tries to read the chip but return the last value that was written...
>> 
>> If I return false for readable_reg I get an errno = -5 for all reads.
>> If I return true, I get:
>> 
>> [   13.353654] leds-is31fl319x 4-0064: is31fl319x_brightness_set read ret=-11 [1]: 0
>> 
>> [   27.661668] leds-is31fl319x 4-0064: is31fl319x_brightness_set read ret=-110 [1]: 0
>> 
>> which means that the regmap *is* trying to read the chip instead of the cache. This
>> times out the bus:
>> 
>> [   27.641615] omap_i2c 4807c000.i2c: controller timed out
>> 
>> Such timeouts lead to kernel stalls if there are led triggers (system is flooded
>> by unprocessed write requests to the chip).
>> 
>> 'top' revealed the highest activity process:
>> 
>> PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
>> 824 root     -51   0       0      0      0 R  41.1  0.0   0:44.59 irq/299-4807c00 
>> 
>> which is indeed the i2c interrupt for the bus where the led driver is connected to.
>> 
>> Please can someone look over the code to spot issues?
>> 
>> http://git.goldelico.com/?p=gta04-kernel.git;a=blob;f=drivers/leds/leds-is31fl319x.c;h=05f89a27a568c1f9a5c55917ca72e34ce905760c;hb=0e74d2f7ab126d4a1b1a6cc2cd082b0a5fc96a5f
> 
> I think I have found the problem. regmap_read returns errno = -5 if the
> register cache access fails.
> 
> And it fails if there is no cache and the register is marked as not readable.
> 
> What I didn't expect is that the default is to have *no cache*.
> 
> And some examples of regmap based drivers seem to run w/o cache on
> i2c or I would have spotted this line:
> 
> 	.cache_type = REGCACHE_FLAT,
> 
> which makes the difference :)

Here is the fixed driver:

http://git.goldelico.com/?p=gta04-kernel.git;a=shortlog;h=refs/heads/work/hns/leds/is31fl3196-v2

> 
> I would give away a kingdom for better documentation and how-tos for kernel
> APIs...
> 
> BR,
> Nikolaus
> 
> _______________________________________________
> Kernel mailing list
> Kernel at pyra-handheld.com
> http://pyra-handheld.com/cgi-bin/mailman/listinfo/kernel