This blog focus on microSD support.

Because I already know it is cd-polling problem, so directly go to source code, see if the polling is supported in this version.

Source code position is at openwrt-21.02.1/target/linux/ramips/files/drivers/mmc/host/mtk-mmc/sd.c

... line 2249 ...
if (of_property_read_bool(pdev->dev.of_node, "mediatek,cd-poll"))
    mmc->caps |= MMC_CAP_NEEDS_POLL;

... line 442 ...
if (host->mmc->caps & MMC_CAP_NEEDS_POLL)
    inserted = 1;

... line 1862 ...
if (host->mmc->caps & MMC_CAP_NEEDS_POLL)
    present = 1;

Looks like my patch is already combined to 21.02, so once I add this mediatek,cd-poll to VoCore2 Ultimate DTS it will just works.

We can directly modify openwrt-21.02.1/target/linux/ramips/dts/mt7628an_vocore_vocore2.dts to make VoCore2 support SD card. For simple, attach four lines to end of the dts file.

&sdhci {
	status = "okay";
	mediatek,cd-poll;
};

Now, after this patch, make sure kmod-mmc, kmod-sdhci-mt7620 is selected in kernel.

Compile OpenWrt, then upload to VoCore2, it just works.

PS: if your VoCore do not have SD card slot, enable sdhci polling mode will cause it output error log every two seconds. So this driver is not default enable in VoCore2 device tree.

OpenWrt 21.02.2 is pretty stable, the even better part is it supports WPA3. Official OpenWrt 21.02.2 release directly work with VoCore2 SBC version, but for VoCore2 Ultimate version, we have some external devices need to be supported, so this blog and following blogs I will write down the process I patch OpenWrt 21.02.

There are three main parts:

1. microSD card can not detect or read.
2. ES8388 sound card can not work.
3. DTS(device tree) need to update add 1,2 setting.

In my experience, microSD problem is mainly caused by default mmc driver who do not support cd-polling. cd-polling is used to scan the microSD card insert into the slot but not using card detect pin. Actually I have already submit this patch to 18.06 and 19.07, so I just need to copy and paste the patch to make it work on 21.02.

ES8388 sound card driver code is already in Linux system. For 19.07 I have a dirty patch. The better way is to write a simple clock control driver, and use DTS to setup it. For this version, I will try to make it.

DTS, this is pretty painful to learn because current tutorial is not very friendly for beginner. I will try to write another not that painful tutorial…