About changing "Selected Driver Strength" field of HS_TIMING [185] of eMMC device

[yasushihasegawa]

Dear Community members,

Our customer is mass producing using i.MX7Solo and Android's "IMX6_M6.0.1_2.1.0".
Customer is verifying that the eMMC device will be revised.

They refer to:
myandroid/kernel_imx/Documentation/devicetree/bindings/mmc/mmc.txt

From the above file they confirmed the following contents.
-----------------
Example with sdio function subnode:

mmc3: mmc@01c12000 {
#address-cells = <1>;
#size-cells = <0>;

pinctrl-names = "default";
pinctrl-0 = <&mmc3_pins_a>;
vmmc-supply = <&reg_vmmc3>;
bus-width = <4>;
-----------------

[Customer's Requirement]
The customer wants to change the [Selected Driver Strength] field of HS_TIMING [185] of the eMMC device.

[Question.1]
How can the customer fulfill the above requirement by writing it in the ".dts" file?

[Questino.2]
Take the following .dts file as an example.
Android/kernel_imx/arch/arm/boot/dts/imx7d-sdb.dts
-----
&usdhc3 {
pinctrl-names = "default", "state_100mhz", "state_200mhz";
pinctrl-0 = <&pinctrl_usdhc3>;
pinctrl-1 = <&pinctrl_usdhc3_100mhz>;
pinctrl-2 = <&pinctrl_usdhc3_200mhz>;
assigned-clocks = <&clks IMX7D_USDHC3_ROOT_CLK>;
assigned-clock-rates = <400000000>;
bus-width = <8>;
non-removable;
status = "okay";
};
-----
For example, where is the source code where "bus-width = <8>;" is executed?
Customer is also thinking about source code modification.

Best Regards,

Yasushi Hasegawa

[igorpadykov]

Hi Yasushi

>>[Question.1] How can the customer fulfill the above requirement by writing it in the ".dts" file?

not, sorry

>>[Questino.2]

for understanding mmc driver one can look at its description in Chapter 32 MMC/SD/SDIO Host Driver

attached Linux Manual.

>>where is the source code where "bus-width = <8>;" is executed?

one can look at linux mmc driver sources:

"bus-width" in function mmc_of_parse()
https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/mmc/core/host.c?h=imx_4.1.15_2.0.0...
esdhc_pltfm_set_bus_width(),
https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/mmc/host/sdhci-esdhc-imx.c?h=imx_4...

Best regards
igor
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