Re: [PATCH v5 03/12] mmc: sdhci-msm: add pltfm_data support to get clk-rates from DT

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Hi Rob

On 10/11/2016 12:59 AM, Rob Herring wrote:
On Mon, Oct 10, 2016 at 11:07 AM, Ritesh Harjani <riteshh@xxxxxxxxxxxxxx> wrote:
Hi Rob,

Thanks for review.

On 10/10/2016 6:27 PM, Rob Herring wrote:

On Wed, Oct 05, 2016 at 08:10:31PM +0530, Ritesh Harjani wrote:

This adds support for sdhc-msm controllers to get supported
clk-rates from DT. sdhci-msm would need it's own set_clock
ops to be implemented. For this, supported clk-rates needs
to be populated in sdhci_msm_pltfm_data.

Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxxx>
---
 .../devicetree/bindings/mmc/sdhci-msm.txt          |  1 +
 drivers/mmc/host/sdhci-msm.c                       | 48
++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/Documentation/devicetree/bindings/mmc/sdhci-msm.txt
b/Documentation/devicetree/bindings/mmc/sdhci-msm.txt
index 485483a..6a83b38 100644
--- a/Documentation/devicetree/bindings/mmc/sdhci-msm.txt
+++ b/Documentation/devicetree/bindings/mmc/sdhci-msm.txt
@@ -17,6 +17,7 @@ Required properties:
        "iface" - Main peripheral bus clock (PCLK/HCLK - AHB Bus clock)
(required)
        "core"  - SDC MMC clock (MCLK) (required)
        "bus"   - SDCC bus voter clock (optional)
+- clk-rates: Array of supported GCC clock frequencies for sdhc, Units -
Hz.


Why can't some combination of assigned-clock-rates and querying the
clock provider for rates be used here?

From what I understood, assigned-clock-rates would only work for setting
some default clock rates for certain clocks by calling
of_clk_set_defaults.

Whereas the requirement here is -
That since SDHC msm directly controls the clk(core clock) at source, it's
sdhci-msm driver needs to know the supported clk-rates by the underlying
platform to configure the nearest floor value supported on this platform
(when the request arrives from the core layer to switch the clock).

Why does clk_round_rate not work for you? That will round down to the
nearest frequency supported.
clk_round_rate will round off to nearest supported "ceil" frequency.
But we require nearest rounded off "floor" frequency.


Hence the table of clk-rates is provided for sdhci-msm.


Minimally this would need unit suffix and either be made common or have
a vendor prefix.

Sure will this work in that case - "qcom-clk-rates"

"qcom,clk-rates", but I'm not yet convinced this is right.

Rob
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