On Tuesday 10 December 2013, Dinh Nguyen wrote: > On 12/5/13 2:57 PM, Arnd Bergmann wrote: > > And in now way should the clock provider code look into the DT properties of the > > clock consumer. From what I can tell, the dw-mshc code already interprets the > > "samsung,dw-mshc-sdr-timing" property and uses the data to pass the correct > > clock rate using 'clk_set_rate()'. The clock code should only use the data passed > > in the argument to that function to set up the registers and not need to know > > at all who is setting it. > You're right, the dw-mshc code interprets "samsung,dw-mshc-sdr-timing", > but it is > currently doing it in the platform specific code(dw_mmc-exynos and > dw_mmc-socfpga). > I was thinking I can remove the platform specific for SOCFPGA. But > perhaps now that > patch "mmc: dw_mmc: Make the use of the hold reg generic" is > progressing, and > that patch reads "samsung,dw-mshc-sdr-timing" in the generic dw_mmc > code, I can now > pass it through the clk_set_rate call. Ok, good. > My initial thought to read "samsung,dw-mshc-sdr-timing" in the socfpga clock > driver's was that the SOCFPGA's sdmmc_clk only role in life is to feed > the sdmmc block. So > reading the phase shift bits that adjust this clock does seem weird, but > a straightforward way > of doing it. I stuck it in the function in .prepare function because the > setting of the clock's phase > shift also requires that CIU clock be turned off while the bits are > toggled, so the prepare function > seems to work perfectly. So I think you're only concern is that I should > figure out a way to pass > the values of "samsung,dw-mshc-sdr-timing" from the dw_mmc driver to the > clock driver, correct? > > Yes, I can read the "samsung,dw-mshc-sdr-timing" in the dw_mmc code and > pass it to the clock > driver using clk_set_rate(), but this method seems more cumbersome, as > this clk_set_rate does not > have anything to do with setting the rate, but only the phase shift > settings of the clock. I see, that does indeed sound a bit strange and is probably not the best API. I'm not that familiar with what is actually going on at the hardware level. Can you explain in a little more detail what the phase setting is about? What are the possible values here and what units are being used? > > I am a little confused though what the SYSMGR_SDMMCGRP_CTRL_OFFSET register actually > > does. It looks like this is just a clock divider, which should be represented as > > a separate clock node (as you had in v3) and compute the correct factor from the > > requested clock rate and the parent clock rate. > The SYSMGR_SDMMCGRP_CTRL_OFFSET is just putting the 2 values of > "samsung,dw-mshc-sdr-timing" > into a a single u32 value to be written to the register. > "samsung,dw-mshc-sdr-timing" has 2 values that > controls the phase shift of 2 clocks, the drive clock and the sample clock. Do other clocks ever have the same requirement? Would it make sense to have a generic clk_set_phase interface for this? If not, could the values alternatively (i.e. departing from the samsung method) be encoded in the clock specifier? That would come down to setting #clock-cells = <2> for this clock and using a complex clock in the mshc node to point at it using <&phandle $phase1 $phase2> Arnd Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
