On Tue, 13 Jun 2023 19:29:19 +0200, Mark Brown wrote:
On Tue, Jun 13, 2023 at 07:05:21PM +0200, Takashi Iwai wrote:
Mark Brown wrote:
Oh, I'm afraid that we're seeing different things. The code there is rather to *set* some initial value for each amp register (but only once), and it's not about optimization for writing a same value again.
That is, the function helps to set an initial (mute) value on each amp when the driver parses the topology and finds an amp. But if the driver already has parsed this amp beforehand by other paths, it skips the initialization, as the other path may have already unmuted the amp.
So it is possible that we might set two distinct values during setup then and we're doing this intentionally? It's not obvious that this might happen. A comment wouldn't hurt, and a big part of this is confusing is that in the non-regmap case all we're doing is suppressing duplicate writes, in that path it's just checking for changes in the register value.
None of this is what the non-regmap path does, it just suppresses noop writes to the hardware.
Actually, many of HD-audio codec driver code heavily relies on the regmap, more or less mandatory. The snd_hda_codec_amp_init() is one of such. You may write a codec driver without the regmap, but some helpers won't work as expected.
Sounds like it might be so thinly used it's becoming mandatory to have a regmap in order to avoid gotchas like there might be with things getting muted?
It's rather historical reasons. The caching mechanism was already present and mandatory from the beginning, but it was implemented in a different way. Later on, it was translated to the regmap. Meanwhile, we generalized the HD-audio codec driver to be on a generic HD-audio bus, and this allowed the use without regmap. So some basic helpers are designed to work without regmap but some are still tightly tied with regmap.
Takashi