On 12/01/2013 01:38 AM, Jean Delvare wrote:
[ ... ]
# Note the power up default is actually mode 4, which is even more
# confusing (sysfs would tell you we're in mode 3, until you first
# touch the mode, then it would lock back into mode 1 behavior.
# For the above I made things less confusing for the reader by
# first forcing mode 1.)
Mode "FAN_SET" is problematic on its own, independent of the bug you
found and fixed. There is no room for it in our standard sysfs
interface. It's not really an automatic fan speed mode so it shouldn't
have value >= 2. The closest standard mode would be 0, except that 0 is
supposed to mean "100%", not "some arbitrary initial value". Well, we
could write 0xf to register 0x90 bits 3..0 (assuming they are writable
as the datasheet says) to force the 100% but then this would prevent
the user from returning to the initial state, plus I'm not sure what
would happen at suspend/resume or reboot.
OTOH, if we stick to value 4 for this mode, then there's no reason to
not let the user switch back to it. Supporting it would be truly
trivial.
Another possibility would be to hide this mode, by transparently
switching to the equivalent speed in manual control mode when the
driver is loaded. Then only modes 1, 2 and 3 would be visible to the
user. To be honest I'm not sure why the chip maker didn't implement it
this way in the first place. I think this option has my preference.
Guenter, what do you think? Do we have any precedent?
Hi Jean,
The asc7621 driver uses pwmX_enable=0 to turn the fan off, and =255 to set
it to full speed. I would not necessarily take that as good example, though.
Your proposal to hide FAN_SET underneath mode 1 would be one possibility.
I would also not mind using pwmX_enable=0 ('disabled') for that purpose,
ie let the fan speed revert to the pre-programmed speed instead of 100%
if it is set. While not following the ABI to the letter, one could argue
that it follows the idea.
Thanks,
Guenter
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