On 2015-10-30 09:53, James Cameron wrote:
On Fri, Oct 30, 2015 at 09:36:39AM +0100, David Henningsson wrote:
On 2015-10-30 03:36, Mark Brown wrote:
On Tue, Oct 13, 2015 at 09:07:20AM +0200, David Henningsson wrote:
On 2015-10-12 22:59, James Cameron wrote:
James, please don't drop CCs (this is the convention for kernel lists).
I personally believe that if the physical hardware can be set to state where
it's bricked, the hardware itself is buggy.
If the hardware is buggy, this should be worked around in BIOS or whatever
firmware is present on the machine. Otherwise there is a bug in BIOS.
This is just not possible for most systems, there is no BIOS only a
bootoloader which hands off control to the kernel and stops running at
that point.
The BIOS can poke the hardware, set registers in such ways that
volumes are limited. Registers that the kernel never touches.
I'm not sure how that would work. The BIOS developers and the kernel
developers would have to agree on what registers are to be touched by
the BIOS only. In my case, with the rt5631, the registers could not
be easily isolated in that fashion. And if the kernel hit the reset
bit in one of the registers, whatever the BIOS had set would be lost.
Oh, and power management. The codec can be powered down by suspend,
with the BIOS uninvolved in resume.
The way it has come to work on HDA is that the codec vendor has a number
of "secret" registers, which they only tell the BIOS developers about,
and (to our frustration) are quite reluctant to tell us about.
And certainly the BIOS is involved in setting these registers on S3
resume, too.
One could imagine having ACPI calls for putting a codec in
suspend/resume, but as I said, in many cases (such as yours) this just
makes things more complicated. It's better dealt with in the kernel
codec driver instead.
From
my knowledge, this is more common than not on modern laptops with
HDA codecs. A bootloader could potentially do the same - but in many
embedded setups I suspect it makes just as much sense to do that
during driver initialization instead.
--
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic
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