[PATCH V3 13/14] ARM: dts: stm32: Adjust PLL4 settings on AV96

Patrick DELAUNAY patrick.delaunay at st.com
Wed Apr 1 12:24:07 CEST 2020

Hi Gerald and Manivannan,

> From: Marek Vasut <marex at denx.de>
> Sent: mardi 31 mars 2020 19:52
> The PLL4 is supplying SDMMC12, SDMMC3 and SPDIF with 120 MHz and
> FDCAN with 96 MHz. This isn't good for the SDMMC interfaces, which can not
> easily divide the clock down to e.g. 50 MHz for high speed SD and eMMC
> devices, so those devices end up running at 30 MHz as that is 120 MHz / 4.
> Adjust the PLL4 settings such that both PLL4P and PLL4R run at 100 MHz
> instead, which is easy to divide to 50MHz for optimal operation of both SD and
> eMMC, SPDIF clock are not that much slower and FDCAN is also unaffected.
> Reviewed-by: Patrice Chotard <patrice.chotard at st.com>
> Reviewed-by: Patrick Delaunay <patrick.delaunay at st.com>
> Signed-off-by: Marek Vasut <marex at denx.de>
> Cc: Manivannan Sadhasivam <manivannan.sadhasivam at linaro.org>
> Cc: Patrick Delaunay <patrick.delaunay at st.com>
> Cc: Patrice Chotard <patrice.chotard at st.com>
> ---
> V2: Move this patch before the split of AV96 into SoM and carrier
> V3: No change
> ---

This patch update the PLL4 frequency used on AV96 board,
with different of reference clock tree used on ST board,
this new setting allow to optimize the SDMMC frequency (50MHz vs 30Mz).

I don't know why the previous PLL4 frequency was chosen as a compromise
on reference clock-tree  (PLL4 is used by mostly all the peripheral,
with display and audio requirements).

Can you cross check the proposed clock tree and ack this patch
if these ST requirements are not applicable on AV96 board.

Anyway the code is correct.

Reviewed-by: Patrick Delaunay <patrick.delaunay at st.com>



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