Re: [PATCH v6 7/9] clk: mediatek: Add subsystem clocks of MT8173

[James Liao]

Hi Sascha,

On Thu, 2015-08-06 at 10:53 +0200, Sascha Hauer wrote:
> On Thu, Aug 06, 2015 at 04:23:51PM +0800, James Liao wrote:
> > On Wed, 2015-08-05 at 08:46 +0200, Sascha Hauer wrote:
> > > On Tue, Aug 04, 2015 at 04:16:56PM +0800, James Liao wrote:
> > > >  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.
> > 
> > As I know all constants will be calculated in compile time, so there
> > should be no difference between 51.975 * MHZ and 51975 * KHz. 
> > 
> > > 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?
> > 
> > Here is the clock hierarchy between lvdspll and lvds_pxl:
> > 
> >             --------       AD_VPLL_DPIX_CK  --------   lvds_pxl  -----
> >            |        |--------------------->|        |---------->|
> >            |        |                      | cksys  |           |
> > LVDSPLL -->| LVDSTX |                      | buffer |           | MMSYS
> >            |        | AD_LVDSTX_CLKDIG_CTS | test   |  lvds_cts |
> >            |        |--------------------->|        |---------->|
> >             --------                        --------             -----
> > 
> > Some clocks and blocks are not modeled into CCF. But we prefer to enable
> > lvdspll before enabling lvds_pxl. So I modeled lvds_pxl (and lvds_cts)
> > as a fixed-rate clock with a source from lvdspll.
> > 
> > The frequency of these fixed-rate clocks (such as 148.5 MHz) are typical
> > rate. In fact, we don't care about the actual rate of these clocks. We
> > just care about the enable / disable sequence of them.
> 
> Please either use the real rate or 0 (along with a explaining why). Using
> a frequency with four to five significant digits makes me think that the
> actual rate is very important.

Oops, your suggestion is much different from Daniel's.

Daniel, could you help to comment about how we model these clocks?


Best regards,

James


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/