Re: [Qemu-devel] [PATCH for-3.0 1/1] hw/sd/omap_mmc: Split 'pseudo-reset' from 'power-on-reset'

[Peter Maydell <peter.maydell@linaro.org>]

On 6 July 2018 at 17:21, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
> DeviceClass::reset models a "cold power-on" reset which can
> also be use to powercycle a device; but there is no "hot reset"
> (a.k.a. soft-reset) method available.
>
> The OMAP MMC Power-Up Control bit is not designed to powercycle
> a card, but to disable it without powering it off (pseudo-reset):
>
>   Multimedia Card (MMC/SD/SDIO) Interface [SPRU765A]
>
>   MMC_CON[11] Power-Up Control (POW)
>   This bit must be set to 1 before any valid transaction to either
>   MMC/SD or SPI memory cards.
>   When 1, the card is considered powered-up and the controller core
>   is enabled.
>   When 0, the card is considered powered-down (system dependent),
>   and the controller core logic is in pseudo-reset state. This is,
>   the MMC_STAT flags and the FIFO pointers are reset, any access to
>   MMC_DATA[DATA] has no effect, a write into the MMC.CMD register
>   is ignored, and a setting of MMC_SPI[STR] to 1 is ignored.

This text says that the card "is considered powered-down (system
dependent)", so it's not entirely invalid to reset the card here.
Still, if the guests get confused by it I guess that the n8x0
systems didn't do that, and certainly resetting the other parts
of the controller state is wrong.

Strictly I guess we should also check the enable flag for the other
things this text calls out:
 * accesses to MMC_DATA[DATA]
 * writes to MMC.CMD (we already do this)
 * setting MMC_SPI[STR] to 1 (we don't emulate MMC_SPI)

but we should probably consider that a separate bug. (And the
n8x0 boards are pretty much unmaintained currently, so I don't
care very much whether we fix it or not. I don't have any working
test images -- I have one of uncertain vintage which seems to
be flaky when it gets to the mmc card init, but I think it
makes a bit more progress with this patch now.)

Applied to target-arm.next, thanks.

thanks
-- PMM