On 04/10/2013 04:38 AM, Devin Heitmueller wrote:
On Tue, Apr 9, 2013 at 8:45 PM, Antti Palosaari <crope@xxxxxx> wrote:
Yes, most devices do that, but not all!
MxL5007t has a special register for setting register to read. Look the code
and you could see it easily. It was over year ago I fixed it...
That sounds kind of insane, but I haven't looked at the datasheets and
if Mike Ack'd it, then so be it.
Further, it *should* be done in a single call to i2c_transfer() or
else you won't hold the lock and you will create a race condition.
No. That's why I added new lock. Single i2c_transfer() means all messages
are done using repeated START condition.
No need to add a new lock to your bridge driver. You can just use
__i2c_transfer() and i2c_lock_adapter(state->i2c). That's what
they're doing in the drx-k driver for just such cases where they need
the lock to span multiple calls to i2c_transfer().
Thanks for the tip. It could be cleaner way to do it like that and
likely I will change it after quick check.
I don't need to lock whole adapter, only unsure there is none changing
"register to read" value (stored to special register) before I read it.
So I have to ensure I could do normal writes without a unneeded waiting
- even those happens just between that two phase read.
This sounds more like it's a bug in the i2c master rather than the 5007
driver.
No.
Do you have i2c bus traces that clearly show that this was the cause
of the issue? If we need to define something as "broken" behavior, at
first glance it looks like the way *you're* proposing is the broken
behavior - presumably to work around a bug in the i2c master not
properly supporting repeated start.
Yes and no. I made own Cypress FX2 firmware and saw initially that issue
then. Also, as you could see looking the following patches I ensured /
confirmed issue using two different I2C adapters (AF9015 and AF9035). So I
have totally 3 working adapters to prove it (which are broken without that
patch)!
The whole think sounds screwed up, and without a real i2c trace of the
bus we'll never know. That said, I'm not really in a position to
dispute it given I don't have any devices with the chip in question.
I would suggest renaming the configuration value to something less
controversial, such as "use_repeated_start_for_reads" and avoid using
terms like broken where it's not clear that's actually the case.
It is 100% clearly broken :-] And MxL5007t will not reply correct value.
It returns 0x3f for chip ID. I didn't tested it, but quite good theory
is that there is some other than chip id reg to set special register
when that happens.
I have tested it with 3 devices and there is two devices to left which
are using that new parameter.
regards
Antti
--
http://palosaari.fi/
--
To unsubscribe from this list: send the line "unsubscribe linux-media" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
