On Wed, Aug 5, 2015 at 3:36 PM, Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> wrote:
> On Wed, Aug 05, 2015 at 03:26:29PM +0800, Daniel Kurtz wrote:
>> On Wed, Aug 5, 2015 at 2:46 PM, Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> wrote:
>> > On Tue, Aug 04, 2015 at 04:16:56PM +0800, James Liao wrote:
>> >> Most multimedia subsystem clocks will be accessed by multiple
>> >> drivers, so it's a better way to manage these clocks in CCF.
>> >> This patch adds clock support for MM, IMG, VDEC, VENC and VENC_LT
>> >> subsystems.
>> >>
>> >> Signed-off-by: James Liao <jamesjj.liao@xxxxxxxxxxxx>
>> >> ---
>> >> drivers/clk/mediatek/clk-mt8173.c | 267 +++++++++++++++++++++++++++++++++
>> >> include/dt-bindings/clock/mt8173-clk.h | 97 +++++++++++-
>> >> 2 files changed, 361 insertions(+), 3 deletions(-)
>> >>
>> >> diff --git a/drivers/clk/mediatek/clk-mt8173.c b/drivers/clk/mediatek/clk-mt8173.c
>> >> index f37ace6..05335e5 100644
>> >> --- a/drivers/clk/mediatek/clk-mt8173.c
>> >> +++ b/drivers/clk/mediatek/clk-mt8173.c
>> >> @@ -25,6 +25,10 @@ static DEFINE_SPINLOCK(mt8173_clk_lock);
>> >> static const struct mtk_fixed_clk fixed_clks[] __initconst = {
>> >> FIXED_CLK(CLK_TOP_CLKPH_MCK_O, "clkph_mck_o", "clk26m", 400 * MHZ),
>> >> FIXED_CLK(CLK_TOP_USB_SYSPLL_125M, "usb_syspll_125m", "clk26m", 125 * MHZ),
>> >> + FIXED_CLK(CLK_TOP_DSI0_DIG, "dsi0_dig", "clk26m", 130 * MHZ),
>> >> + FIXED_CLK(CLK_TOP_DSI1_DIG, "dsi1_dig", "clk26m", 130 * MHZ),
>> >> + FIXED_CLK(CLK_TOP_LVDS_PXL, "lvds_pxl", "lvdspll", 148.5 * MHZ),
>> >> + FIXED_CLK(CLK_TOP_LVDS_CTS, "lvds_cts", "lvdspll", 51.975 * MHZ),
>> >
>> > I would expect 51975 * KHZ here to avoid fractional numbers. Probably
>> > gcc calculates that during compile time so this will work as expected,
>> > still I'm not sure this is good style to use fractional numbers here.
>>
>> I thought this looked a bit strange too, but for what its worth, these
>> two evaluate correctly:
>>
>> localhost ~ # cat /sys/kernel/debug/clk/clk_summary | grep lvds
>> lvdspll 0 0 149999878
>> 0 0
>> lvds_pxl 0 0 148500000
>> 0 0
>> lvds_cts 0 0 51975000
>> 0 0
>>
>> >
>> > Anyway, on my system lvdspll is running at 150MHz. Are you sure there is
>> > a clock derived from this running at 148.5MHz? Is it really correct to
>> > use a fixed clock here or should it rather be lvdspll directly?
>>
>> I agree it does look strange to have a 51.975 MHz and 148.5 MHz clocks
>> with a 150 MHz PLL as their parent... However, I'm not sure how much
>> this matters? I think the idea here was that these frequencies are
>> best effort "nominal" clock values provided by Mediatek "designers".
>> The important point is that for the hardware to generate these either
>> of these clocks, lvdspll must be enabled.
>
> This assumes that the lvdspll always runs at frequency the designers
> thought that might be a good value. Should we really provide wrong clock
> values when on some board for whatever reason the lvdspll is configured
> for a different frequency?
Do you have an alternative suggestion for estimating the frequency of
a non-software controllable or measurable hardware clock?
Or can we land this series and update the frequency via some future
patch if and when that other board arrives which may have a different
frequency - and there is some reason to care what that frequency
actually is?
-Dan
>
> sascha
>
> --
> Pengutronix e.K. | |
> Industrial Linux Solutions | http://www.pengutronix.de/ |
> Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
> Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
