Il 15/06/23 13:16, Matthias Brugger ha scritto:
On 15/06/2023 11:51, TingHan Shen (沈廷翰) wrote:
Hi AngeloGioacchino,
On Mon, 2023-05-22 at 11:30 +0200, AngeloGioacchino Del Regno wrote:
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Some bootloaders will set MSDCPLL's rate lower than 400MHz: what I have
seen is this clock being set at around 384MHz.
This is a performance concern (and possibly a stability one, for picky
eMMC/SD cards) as the MSDC controller's internal divier will choose a
frequency that is lower than expected, in the end causing a difference
in the expected mmc/sd device's timings.
Make sure that the MSDCPLL frequency is always set to 400MHz to both
improve performance and reliability of the sd/mmc storage.
Fixes: 5d2b897bc6f5 ("arm64: dts: mediatek: Add mt8192 clock controllers")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
---
arch/arm64/boot/dts/mediatek/mt8192.dtsi | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/arm64/boot/dts/mediatek/mt8192.dtsi
b/arch/arm64/boot/dts/mediatek/mt8192.dtsi
index 5c30caf74026..6fc14004f6fd 100644
--- a/arch/arm64/boot/dts/mediatek/mt8192.dtsi
+++ b/arch/arm64/boot/dts/mediatek/mt8192.dtsi
@@ -677,6 +677,8 @@ apmixedsys: syscon@1000c000 {
compatible = "mediatek,mt8192-apmixedsys", "syscon";
reg = <0 0x1000c000 0 0x1000>;
#clock-cells = <1>;
+ assigned-clocks = <&apmixedsys CLK_APMIXED_MSDCPLL>;
+ assigned-clock-rates = <400000000>;
};
systimer: timer@10017000 {
--
2.40.1
Comment from mtk emmc owner,
"As we all know, the clock has some jitter, when we set MSDCPLL to 400M,
but the actual measurement is not exactly 200M.
For eMMC, the spec stipulates that clock cannot exceed 200M.
If MSDCPLL is set to 400M, the actual measurement may exceed the spec.
So we set MSDCPLL to 384M in the bootloader stage to avoid exceeding the spec."
Thanks for the comment,
I haven't seen any issue with this commit, if not a slight performance improvement,
on MT8192 and MT8195, but if there's risk to overclock the card, then it's not ok.
In any case, what is the expected jitter percentage?
eMMC/SD cards do expect jitter by spec anyway.
Thanks,
Angelo
Thanks for the feedback. Given that I'm not aware of any regressions that got fixed
by this commits I will drop this series for now. We can keep on the discussion and
if needed add them in a later stage.
Regards,
Matthias
