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?
sascha
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