Re: [Qemu-arm] [PATCH] hw/arm/raspi: avoid reparenting the sd card during qbus tree reset

[Peter Maydell]

On Wed, 4 Sep 2019 at 17:23, Damien Hedde <address@hidden> wrote:
>
> In the raspi machine, the sd card can be on several sd bus (in reality
> there is one bus but several controllers). It is initially created in
> the "sd-bus" child in the gpio peripheral. Then is moved (parent bus
> changes) during machine reset in the "sdhci-bus". It can be moved again
> by software between the "sdhci-bus" and another bus ("bcm2835-sdhost-bus").
> Here's the corresponding qbus tree of the raspi machine:
>  + sysbus
>    * bcm2835_gpio
>      + sd-bus
>        * sd-card
>    * bcm2835-sdhost
>      + bcm2835-sdhost-bus
>    * generic-sdhci
>      + sdhci-bus
>
> During the initial machine reset, the sd card is moved. Since reset is
> based on qbus tree, moving the card during the reset seems odd (it changes
> the qbus tree). In this case, because of the order the qbus tree is
> walked, the sd card ends up being reset twice; the effective reset order call
> follows:
>  1 sd-card
>  2 sd-bus
>  3 bcm2835_gpio        -> move the sd-card to sdhci_bus
>  4 bcm2835-sdhost-bus
>  5 bcm2835-sdhost
>  6 sd-card             (again)
>  7 sdhci-bus
>  8 generic-sdhci
>
> This patch adds a raspi machine reset method which moves the sd card
> to the sdhci-bus before doing the whole reset (which will try to do the
> move too). By anticipating the move we avoid changing the qdev tree while
> resetting it.
>
> In consequence the step 1 is skipped in the previous list: when reset starts
> the sd-card is already not a child of bcm2835_gpio.

The solution proposed in this patch pushes something that should
really be the business just of the SoC model out to the machine
model level; it would be nice to be able to avoid that.

thanks
-- PMM