On 7/18/08, Mark Brown broonie@opensource.wolfsonmicro.com wrote:
On Fri, Jul 18, 2008 at 03:44:37PM -0400, Jon Smirl wrote:
On 7/18/08, Jon Smirl jonsmirl@gmail.com wrote:
- Something Freescale calls cellphone slave but it is more like clock
distribution.
In cellslave mode one i2s port is in normal slave mode. The clock from this port is used to drive up to three other i2s ports in master mode.
...
When the clock frequency changes I need to notify the i2s drivers for the dependent channels. Do we need a third choice, SND_SOC_CLOCK_SLAVE? Alternatively I can use another clock id value.
Without having looked at how this works in hardware I'd probably implement this by using a different clock id for the slave ports if I wanted to use set_sysclk() to configure cell slave mode. It sounds like you've got to choose between two sources within the SoC, one being that clocked in from the external source and the other regular clocks. From what you're saying as far as the individual I2S port is concerned it is the master in both cases.
That might work better. Currently I was setting cellslave mode at boot time from the device tree. But by using different clock ids it can be set dynamically.
switch (dir) { case SND_SOC_CLOCK_IN: return 0; case SND_SOC_CLOCK_OUT: default: if (!(psc_i2s->sicr & MPC52xx_PSC_SICR_CELLSLAVE)) { /* implement me */ /* compute and set the needed dividers for the internal clock */ return -EINVAL; } psc_i2s->sysclk = freq; return -EINVAL; }}
If you did use a separate clock id then you could set or clear MPC52xx_PSC_SICR_CELLSLAVE as appropriate here which might be a bit easier to write. It depends on what's clearer and what work is needed to configure the slave mode - I guess there may be other configuration required?
Having said that the important thing here is that what you do is sensible and idiomatic for people working on the platform so it may be that what you've got already is the most expressive thing. The clock configuration is done by machine drivers which will obviously be platform specific.