Stephen Boyd <sb...@codeaurora.org> writes: > On 05/09, Eric Anholt wrote: >> If the firmware had set up a clock to source from PLLC, go along with >> it. But if we're looking for a new parent, we don't want to switch it >> to PLLC because the firmware will force PLLC (and thus the AXI bus >> clock) to different frequencies during over-temp/under-voltage, >> without notification to Linux. >> >> On my system, this moves the Linux-enabled HDMI state machine and DSI1 >> escape clock over to plld_per from pllc_per. EMMC still ends up on >> pllc_per, because the firmware had set it up to use that. > > Is it ok for EMMC rate to change with over-temp/under-voltage? > The description makes it sound like PLLC is for clks that want to > run at some system bus rate and they don't care about exact > frequencies.
I'm surprised it's OK for it to change, but the firmware is very intentionally putting it on PLLC (there's this #define for where most peripherals go, and EMMC doesn't use it and goes for PLLC instead). If we do decide we want to override the firmware, I suspect we'll use assigned-clock-parents for that. >> Signed-off-by: Eric Anholt <e...@anholt.net> >> Fixes: 41691b8862e2 ("clk: bcm2835: Add support for programming the audio >> domain clocks") >> diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c >> index 1091012ecec6..1d8f29ea9f69 100644 >> --- a/drivers/clk/bcm/clk-bcm2835.c >> +++ b/drivers/clk/bcm/clk-bcm2835.c >> @@ -1008,16 +1008,28 @@ static int bcm2835_clock_set_rate(struct clk_hw *hw, >> return 0; >> } >> >> +static bool >> +bcm2835_clk_is_pllc(struct clk_hw *hw) >> +{ >> + if (!hw) >> + return false; >> + >> + return strncmp(clk_hw_get_name(hw), "pllc", 4) == 0; > > This strcmp is not great. Any chance we could look for the parent > by reading the hardware and knowing what bit corresponds to pllc > as a parent? That would be much nicer so that we don't rely on > string comparisons for something the hardware can tell us. We just have the parent index, but which indices are pllc dividers is different between bcm2835_clock_per_parents and bcm2835_clock_vpu_parents. So, I guess it's possible, but seems more error-prone than the strncmp.
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