Re: [PATCH v5 10/11] hw/arm: Wire up BMC boot flash for npcm750-evb and quanta-gsj

[Philippe Mathieu-Daudé]

On 7/14/20 6:21 PM, Markus Armbruster wrote:
> Philippe Mathieu-Daudé <f4bug@amsat.org> writes:
> 
>> + qemu-block experts.
>>
>> On 7/14/20 11:16 AM, Markus Armbruster wrote:
>>> Havard Skinnemoen <hskinnemoen@google.com> writes:
>>>
>>>> On Mon, Jul 13, 2020 at 7:57 AM Cédric Le Goater <clg@kaod.org> wrote:
>>>>>
>>>>> On 7/9/20 2:36 AM, Havard Skinnemoen wrote:
>>>>>> This allows these NPCM7xx-based boards to boot from a flash image, e.g.
>>>>>> one built with OpenBMC. For example like this:
>>>>>>
>>>>>> IMAGE=${OPENBMC}/build/tmp/deploy/images/gsj/image-bmc
>>>>>> qemu-system-arm -machine quanta-gsj -nographic \
>>>>>>       -bios ~/qemu/bootrom/npcm7xx_bootrom.bin \
>>>>>>       -drive file=${IMAGE},if=mtd,bus=0,unit=0,format=raw,snapshot=on
>>>>>>
>>>>>> Reviewed-by: Tyrone Ting <kfting@nuvoton.com>
>>>>>> Signed-off-by: Havard Skinnemoen <hskinnemoen@google.com>
>>>>>
>>>>> May be we don't need to create the flash object if dinfo is NULL.
>>>>
>>>> It's soldered on the board, so you can't really boot the board without
>>>> it. But if you think it's better to remove it altogether if we don't
>>>> have an image to load into it, I can do that.
>>>
>>> If a device is a fixed part of the physical board, it should be a fixed
>>> part of the virtual board, too.
>>
>> We agree so far but ... how to do it?
>>
>> I never used this API, does that makes sense?
>>
>>     if (!dinfo) {
>>         QemuOpts *opts;
>>
>>         opts = qemu_opts_create(NULL, "spi-flash", 1, &error_abort);
>>         qdict_put_str(opts, "format", "null-co");
>>         qdict_put_int(opts, BLOCK_OPT_SIZE, 64 * MiB);
>>         qdict_put_bool(opts, NULL_OPT_ZEROES, false); // XXX
>>
>>         dinfo = drive_new(opts, IF_MTD, &error_abort);
>>         qemu_opts_del(opts);
>>     }
> 
> I believe existing code special-cases "no backend" instead of making one
> up.
> 
> Example: pflash_cfi0?.c
> 
> If ->blk is non-null, we read its contents into the memory buffer and
> write updates back, else we leave it blank and don't write updates back.
> 
> Making one up could be more elegant.  To find out, you have to try.

I'd rather avoid ad-hoc code in each device. I2C EEPROM do that too,
it is a source of head aches.

>From the emulation PoV I'd prefer to always use a block backend,
regardless the user provide a drive.

> 
> We make up a few default drives (i.e. drives the user doesn't specify):
> floppy, CD-ROM and SD card.  Ancient part of the user interface, uses
> DriveInfo.  I doubt we should create more of them.
> 
> I believe block backends we make up for internal use should stay away
> from DriveInfo.  Kevin, what do you think?  How would you make up a
> null-co block backend for a device's internal use?

I read 'DriveInfo' is the legacy interface, but all the code base use it
so it is confusing, I don't understand what is the correct interface to
use.

> 
>> We should probably add a public helper for that.
> 
> If we decide we want to make up backends, then yes, we should do that in
> a helper, not in each device.
> 
>> 'XXX' because NOR flashes erase content is when hardware bit
>> is set, so it would be more useful to return -1/0xff... rather
>> than zeroes.
> 
>