Re: [RFC PATCH 03/14] hw/misc/bcm2835_property: Handle the 'domain state' property

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

On 9/29/19 9:01 AM, Esteban Bosse wrote:
> El mié, 04-09-2019 a las 19:13 +0200, Philippe Mathieu-Daudé escribió:
>> The kernel is happy with this change, so we don't need
>> to do anything more sophisticated.
>>
>> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> ---
>>   hw/misc/bcm2835_property.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/hw/misc/bcm2835_property.c b/hw/misc/bcm2835_property.c
>> index 399f0d9dd5..d8eb28f267 100644
>> --- a/hw/misc/bcm2835_property.c
>> +++ b/hw/misc/bcm2835_property.c
>> @@ -127,6 +127,14 @@ static void
>> bcm2835_property_mbox_push(BCM2835PropertyState *s, uint32_t value)
>>               resplen = 8;
>>               break;
>>   
>> +        case 0x00030030: /* Get domain state */
>> +            qemu_log_mask(LOG_UNIMP,
>> +                          "bcm2835_property: 0x%08x get domain state
>> NYI\n",
>> +                          tag);
>> +            /* FIXME returning uninitialized memory */
>> +            resplen = 8;
>> +            break;
>> +
>>           case 0x00038002: /* Set clock rate */
>>           case 0x00038004: /* Set max clock rate */
>>           case 0x00038007: /* Set min clock rate */
> 
> Searching this property in the kernel, I found a lot of properties not
> implemented.
> https://github.com/raspberrypi/linux/blob/rpi-4.19.y/include/soc/bcm2835/raspberrypi-firmware.h#L41
> Are the properties only added when they are necessaries for the
> standard kernel use?

Yes, the idea is to emulate the bare minimum required to run your guest 
code. To test this series I used the closed source kernel provided by 
the Raspberry Pi foundation [1] which the one that does the most of 
UNIMP accesses, the Debian trunk one and I build one from [2].

The problem is old kernels don't support the raspi4, and recent kernels 
do a lot of property calls to use recent features.

A "property call" is a call from the ARM core to the VideoCore firmware, 
like a Remote Procedure Call. The ARM core write some 
arguments/structure to a memory space shared with the VideoCore, use a 
MailBox to send a 'property' key to the VideoCore and wait/poll for a 
response from the VC. The VC handles the 'property' call, if required 
fills the structure in the same memory space the ARM used, then reply 
via another MailBox channel to notify the ARM core.

QEMU does not model the VideoCore. Instead we directly fill the memory 
from the ARM property call. We fake the VC firmware.

[1] https://github.com/raspberrypi/firmware/blob/master/boot/kernel8.img
[2] https://github.com/raspberrypi/linux/tree/rpi-5.3.y