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Re: [PATCH 06/11] Documentation: mmc: sdhci-of-arasan: Add ability to export card clock

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Rob,

On Wed, Jun 8, 2016 at 1:19 PM, Rob Herring <robh@kernel.org> wrote:
> On Tue, Jun 07, 2016 at 03:44:39PM -0700, Douglas Anderson wrote:
>> Some SD/eMMC PHYs (like the PHY from Arasan that is designed to work
>> with arasan,sdhci-5.1) need to know the card clock in order to function
>> properly.  Let's expose this clock using a standard device tree
>> mechanism so that the PHY can get access to and query the card clock.
>
> Need to know the clock freq or need the clock? The former doesn't need
> to be in DT.

The PHY needs to know the card clock frequency.  This clock clock
frequency is known nowhere else in the system except the SDHCI driver
since the SDHCI component takes its input clock and applies some
dividers to get the card clock.  In silicon, the SDHCI component and
the PHY are separate and there is a physical clock signal going from
the SDHCI component to the PHY component, so modeling this as a clock
in in the device tree seems sane, doesn't it?

-Doug

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[PATCH 0/11] Changes to support 150 MHz eMMC on rk3399 Douglas Anderson <dianders@chromium.org> - 2016-06-08 00:50 +0200
  [PATCH 06/11] Documentation: mmc: sdhci-of-arasan: Add ability to export card clock Douglas Anderson <dianders@chromium.org> - 2016-06-08 00:50 +0200
    Re: [PATCH 06/11] Documentation: mmc: sdhci-of-arasan: Add ability  to export card clock Rob Herring <robh@kernel.org> - 2016-06-08 22:20 +0200
      Re: [PATCH 06/11] Documentation: mmc: sdhci-of-arasan: Add ability to  export card clock Doug Anderson <dianders@chromium.org> - 2016-06-08 23:00 +0200
        Re: [PATCH 06/11] Documentation: mmc: sdhci-of-arasan: Add ability  to export card clock Rob Herring <robh@kernel.org> - 2016-06-10 15:20 +0200
  [PATCH 05/11] arm64: dts: rockchip: Add soc-ctl-syscon to sdhci for rk3399 Douglas Anderson <dianders@chromium.org> - 2016-06-08 00:50 +0200
  [PATCH 01/11] phy: rockchip-emmc: Increase lock time allowance Douglas Anderson <dianders@chromium.org> - 2016-06-08 00:50 +0200
  [PATCH 10/11] phy: rockchip-emmc: Minor code cleanup in rockchip_emmc_phy_power_off() Douglas Anderson <dianders@chromium.org> - 2016-06-08 00:50 +0200
  [PATCH 09/11] phy: rockchip-emmc: Set phyctrl_frqsel based on card clock Douglas Anderson <dianders@chromium.org> - 2016-06-08 00:50 +0200
  [PATCH 04/11] mmc: sdhci-of-arasan: Properly set corecfg_baseclkfreq on rk3399 Douglas Anderson <dianders@chromium.org> - 2016-06-08 00:50 +0200
  [PATCH 08/11] Documentation: phy: Let the rockchip eMMC PHY get an exported card clock Douglas Anderson <dianders@chromium.org> - 2016-06-08 00:50 +0200
    Re: [PATCH 08/11] Documentation: phy: Let the rockchip eMMC PHY get  an exported card clock Rob Herring <robh@kernel.org> - 2016-06-10 15:40 +0200
  [PATCH 07/11] mmc: sdhci-of-arasan: Add ability to export card clock Douglas Anderson <dianders@chromium.org> - 2016-06-08 00:50 +0200

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