Re: [PATCH v5 01/11] hw: arm: Add bananapi M2-Ultra and allwinner-r40 support

[Peter Maydell]

On Fri, 23 Jun 2023 at 20:33, Guenter Roeck <linux@roeck-us.net> wrote:
>
> On 6/23/23 10:44, Peter Maydell wrote:
> > On Sat, 17 Jun 2023 at 17:29, Guenter Roeck <linux@roeck-us.net> wrote:
> >>
> >> Hi,
> >>
> >> On Tue, May 23, 2023 at 06:04:58PM +0800, qianfanguijin@163.com wrote:
> >>> From: qianfan Zhao <qianfanguijin@163.com>
> >>>
> >>> Allwinner R40 (sun8i) SoC features a Quad-Core Cortex-A7 ARM CPU,
> >>> and a Mali400 MP2 GPU from ARM. It's also known as the Allwinner T3
> >>> for In-Car Entertainment usage, A40i and A40pro are variants that
> >>> differ in applicable temperatures range (industrial and military).
> >>>
> >>> Signed-off-by: qianfan Zhao <qianfanguijin@163.com>
> >>> Reviewed-by: Niek Linnenbank <nieklinnenbank@gmail.com>
> >>
> >> I tried this in mainline linux with the following command.
> >>
> >> qemu-system-arm -M bpim2u \
> >>          -kernel arch/arm/boot/zImage -no-reboot \
> >>          -snapshot -drive file=rootfs-armv7a.ext2,format=raw,if=sd \
> >>          -nic user \
> >>          --append "root=/dev/mmcblk0 rootwait console=ttyS0,115200" \
> >>          -dtb arch/arm/boot/dts/sun8i-r40-bananapi-m2-ultra.dtb \
> >>          -nographic -monitor null -serial stdio
> >>
> >> Main problem is that the SD card gets instantiated randomly to
> >> mmc0, mmc1, or mmc2, making it all but impossible to specify a
> >> root file system device. The non-instantiated cards are always
> >> reported as non-removable, including mmc0. Example:
> >>
> >> mmc0: Failed to initialize a non-removable card
> >
> > Do you mean that QEMU randomly connects the SD card to
> > a different MMC controller each time, or that Linux is
> > randomly assigning mmc0 to a different MMC controller each
> > time ?
> >
>
> Good question. Given the workaround (fix ?) I suggested is
> in the devicetree file, I would assume it is the latter. I suspect
> that Linux assigns drive names based on hardware detection order,
> and that this is not deterministic for some reason. It is odd
> because I have never experienced that with any other emulation.

Yeah, I don't really understand why it would be non-deterministic.
But it does make it sound like the right thing is for the
device tree file to explicitly say which MMC controller is
which -- presumably you might get unlucky with the timing
on real hardware too.

> A secondary problem may be that Linux thinks that the first
> drive is not removable, even though it is a SD drive. I  think
> that is a problem with qemu, but I don't understand the qemu
> code well enough to understand why. It seems that the mmc
> capability register always has bit 8 set, even for the first
> drive, but I don't know where/how that is set and how to
> change it. SDHCI has the capareg property, but that isn't
> used here (or I don't know how to use/set it).

Yeah, this seems likely to be something we're getting wrong.
I assume on other QEMU boards the SD card appears as
removeable ?

thanks
-- PMM