On Tue, Sep 29, 2015 at 02:34:33PM -0700, Anatol Pomozov wrote:
On Fri, Sep 18, 2015 at 6:54 AM, Mark Brown broonie@kernel.org wrote:
On Mon, Aug 31, 2015 at 01:50:58PM -0700, Anatol Pomozov wrote:
Per discussion at [1] currently there is no clear definition of what is FSYNC polarity. Different drivers use its own definition of what is "normal" and what is "inverted" fsync in different modes. This leads to compatibility problems between drivers.
Please keep changelogs wrapped at under 80 columns as is covered in SubmittingPatches and please write free standing changelogs that don't require reference to external discussions unless there is a strong reason to do so. This makes both the e-mails and the git changelogs easier to read, ensuring that people don't need to go online to read things and links don't go bad.
I see that external links quite actively used by developers: $ git log --grep Link
but no problem, I can inline info into the commit description.
Like I say there can be strong reasons to do this but this doesn't seem to be one of them.
- For FSYNC:
- "normal" polarity means frame starts at rising edge of FSYNC
- "inverted" polarity means frame starts at falling edge of FSYNC
This isn't true (or at least isn't clear) for I2S based modes, normally the left channel is thought of as the first channel sent and the left channel starts on the falling edge of LRCLK, not the rising edge (which signals the start of the right frame).
In the I2S docs/specs I found I2S format has frames like you described
- starts at falling edge, left channel first. Per description above
this will have "negative" FSYNC polarity.
The I2S docs do not define frame polarity. Polarity is purely Linux driver thing and we can choose definition we want.
I don't think that's true, the expectation is that a left/right sample pair is time aligned so the left channel is definitely the start of frame for all meaningful purposes. It's certainly what I'd expect most people to understand - choosing a counterintuitive definition to make this one statement convenient is going to lead to constant confusion for the mode which is clearest.