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From: Peter Maydell <peter.maydell@linaro.org>
Date: Sun, 20 Dec 2015 17:10:03 +0000
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Subject: Re: [Qemu-devel] [PATCH 04/10] hw/sd: Add QOM bus which SD cards
	plug in to
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To: Peter Crosthwaite <crosthwaitepeter@gmail.com>
Cc: Kevin O'Connor <kevin@koconnor.net>, Peter Crosthwaite <crosthwaite.peter@gmail.com>, Markus Armbruster <armbru@redhat.com>, Patch Tracking <patches@linaro.org>, QEMU Developers <qemu-devel@nongnu.org>, Alistair Francis <alistair.francis@xilinx.com>, qemu-arm <qemu-arm@nongnu.org>, Paolo Bonzini <pbonzini@redhat.com>, "Edgar E. Iglesias" <edgar.iglesias@gmail.com>

On 19 December 2015 at 21:38, Peter Crosthwaite
<crosthwaitepeter@gmail.com> wrote:
> On Fri, Dec 11, 2015 at 04:37:05PM +0000, Peter Maydell wrote:
>> +bool sdbus_get_inserted(SDBus *sdbus)
>> +{
>> +    SDState *card = get_card(sdbus);
>> +
>> +    if (card) {
>> +        SDClass *sc = SD_GET_CLASS(card);
>> +
>> +        return sc->get_inserted(card);
>> +    }
>> +
>> +    return false;
>> +}
>
> This I am not sure about. Realistically, the card has no self
> awareness of its ejection state so it can't be polled for "are
> you there". The card insertion switch is implemented as a
> physical switch on the slot itself and a property of the bus.
>
> The absence on presence of a device should determine this, making me
> think this should return !!card.
>
> Unfortunately, we have the case of the block UI being able to trigger a
> card ejection from underneath the bus level. But since the SD card is already
> using qdev_get_parent_bus() the removal from the bus can be managed at the
> card level.

For user-level back compat I think we need to retain "might have
an sdcard object with no block backend, and that means
'no-card-present'". This is both for the user facing
monitor commands to manipulate the sd card, and also
for the not-yet-QOMified controllers, which will always
create an sdcard object even if there's no block backend
(which should continue to mean "no card").

thanks
-- PMM