On 07/02/13 03:57, Daniel Drake wrote:
On Mon, Jul 1, 2013 at 3:48 PM, Sebastian Hesselbarth
<sebastian.hesselbarth@xxxxxxxxx> wrote:
I prefer not to try to find the best clock (source) at all. Let the
user pass the clock name by e.g. platform_data (or DT) and just try to
get the requested pixclk or a integer multiple of it. You will never be
able to find the best clock for all use cases.
Just figure out, if integer division is sufficient to get requested
pixclk and clk_set_rate otherwise. This may be useful for current mode
running at 148.5MHz (1080p50) and new mode at 74.25MHz (1080i50, 720p).
I am not opposed to this approach, it is nice and simple, but as
Russell points out we do additionally need to distinguish between
clocks that are "ours" to play with, vs those that are shared with
other devices. It would be a bad idea to try call clk_set_rate() on
the AXI bus clock, for example, changing the clock for a whole bunch
of other devices. This is what the is_dedicated flag is about. However
such a flag could be easily added to the DT/platform data definition
that you propose.
Daniel,
now I got the idea of .is_dedicated. At least for Dove, we could still
implement AXI bus clock as fixed-rate clock, so you cannot mess with it.
I am almost sure, it will hang Dove when you change it, as there are
some devices depending on it (and the correct rate of it). Moreover,
LCDCLK is dedicated to CRTC0/1 so AXICLK is the only clock not
dedicated to LCD controllers.
But I am fine with .is_dedicated - I just think we should not try to
find the best clock source but leave that decision to the user
(=developer, DTS author; not userspace user).
Sebastian
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