Re: [Qemu-devel] [PATCH 6/6] hw/sd.c: convert to QOM object

[Igor Mitsyanko <i.mitsyanko@gmail.com>]

On 02.04.2012 7:48 PM, Peter Maydell wrote:
> On 2 April 2012 15:28, Igor Mitsyanko<i.mitsyanko@samsung.com>  wrote:
>> +    s->card = SD_CARD(object_new(TYPE_SD_CARD));
>>      dinfo = drive_get_next(IF_SD);
>> -    s->card = sd_init(dinfo ? dinfo->bdrv : NULL, 0);
>> +    SD_GET_CLASS(s->card)->init(s->card, dinfo ? dinfo->bdrv : NULL, false);
>
> Ideally rather than having a class specific init function we
> should make the 'is_spi' and 'bdrv' be object properties, and
> then you do something like (syntax probably wrong but):
>    s->card = SD_CARD(object_new(TYPE_SD_CARD));
>    if (dinfo) {
>       object_property_set_bdrv(s->card, dinfo->bdrv, "bdrv", errp);
>    }
>    realize(s->card);
>
> (where the default for bdrv is NULL and the default for is_spi is false
> so we don't need to set that).
>
> This needs realize support for QOM objects, though.
>
> -- PMM
>
>

I absolutely agree, that's how I wanted to do this in my working tree at 
first, but then several issues arose:
1) Pointer properties are obviously interfere with QOM principles, BDRV 
should be a link instead;
2) At first I made SD card child of SD host controller, but it most 
certainly wrong, it should be a link. But where should it be placed, 
under /block-dev/* maybe?
3) There is no point in creating SD card object until user specified an 
image.
4) Not every host controller on specific board is actually active, and 
nothing good will happen if you will try to hot-insert SD card in 
controller which was not activated by kernel. Having a child<SD> 
property in every controller instance is wrong.

What I want to do now is introduce CardSlot object and probably also 
HostControllerClass. Boards will instantiate as much CardSlots as it 
actually has and connect them with SDHC with links. SDCard object will 
be dynamically created and destroyed by setting CardSlot::inserted and 
CardSlot::image properties, SDcards will be childs of CardSlots.
But I havn't figured out how to avoid additional overhead in such a scheme.