How do disable MMC Command Queue Engine

Question

What is the kernel parameter to disable the Command Queue Engine driver?

I am reading through mmc.c

MMC_DEV_ATTR(cmdq_en, "%d\n", card->ext_csd.cmdq_en);
/*
* Enable Command Queue if supported. Note that Packed Commands cannot
* be used with Command Queue.
*/
card->ext_csd.cmdq_en = false;

I am thinking maybe setting the parameter ext_csd.cmdq_en=false I tried this sdhci.debug_quirks=0x65168080 as mentioned here but it doesn't work.

Answer 1

It turns out the device tree has "mediatek,cqhci" property which isn't supported well by the kernel

/dts-v1/;

/ {
    mmc@11230000 {
        compatible = "mediatek,mt6768-mmc";
        mediatek,cqhci;
    };
};

So I had to modify the device tree file with fdtput.

fdtput -d /path/to/fdt /mmc@11230000 "mediatek,cqhci"

Steps

1. I dumped the device tree blob from the boot.img
2. Binwalked the blob to get the pure flattened device tree
3. Deleted the cqhci enabler property from the blob