On Tue, 26 Apr 2016, Lars-Peter Clausen wrote: > On 04/21/2016 04:01 PM, Ricard Wanderlof wrote: > > > > ... > > The problem I have is that the driver assumes that the CODEC has been > > initialized with the default register settings when the system boots. > > However, if the system has not been power cycled but just rebooted, this > > is not necessarily the case, as the CODEC has no external reset pin but > > derives its reset signal internally from the power level. > > ... Sorry I haven't been able to respond earlier. > I've been thinking about this for the last few days trying to come up with a > good solution, but it is really difficult. > > The issue you are describing is simply an oversight from my side. > > One solution would be do drop the register default values and let regmap > fill the register cache on demand when a read is done the first time for a > register. The problem with this approach is that we leave the device in an > unknown state when we probe the driver, but we really want to have it in a > known state of lowest power. > > The alternative is to write out the register defaults when the device is > probed, sort of a poor mans software reset, this brings us into a known > state. This approach has the downside that there is the overhead of having > to write all registers. > > I don't like either, but given the limitations of the hardware we'll have to > choose one and in that case I'd slightly lean towards the later solution has > it gives us consistent and predictable behavior and the overhead of writing > the registers should be manageable. Either way, there will be a fair amount of communication with the codec, either as a result of setting the default values, or as a result of reading the existing ones in order to determine what would be necessary to write. I would think that having the codec in a controlled known (low power) state would tip the balance in favor of the second solution. One question is though should one write out _all_ registers, including those not actually used by the driver? I'm thinking of an upgrade/downgrade situation, where a previously running kernel version has set up a register which the currently running version doesn't need to touch. /Ricard -- Ricard Wolf Wanderlöf ricardw(at)axis.com Axis Communications AB, Lund, Sweden www.axis.com Phone +46 46 272 2016 Fax +46 46 13 61 30 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
