Re: [RFC PATCH 3/6] hw/sd/sdcard: Do not use legal address '0' for INVALID_ADDRESS

[Markus Armbruster]

Philippe Mathieu-Daudé <philmd@redhat.com> writes:

> On 9/21/20 2:24 PM, Dr. David Alan Gilbert wrote:
>> * Markus Armbruster (armbru@redhat.com) wrote:
>>> Philippe Mathieu-Daudé <philmd@redhat.com> writes:
>>>
>>>> +Paolo & Kevin.
>>>>
>>>> On 9/21/20 10:40 AM, Markus Armbruster wrote:
>>>>> Philippe Mathieu-Daudé <f4bug@amsat.org> writes:
>>>>>
>>>>>> As it is legal to WRITE/ERASE the address/block 0,
>>>>>> change the value of this definition to an illegal
>>>>>> address: UINT32_MAX.
>>>>>>
>>>>>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>>>>>> ---
>>>>>> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
>>>>>> Cc: Markus Armbruster <armbru@redhat.com>
>>>>>>
>>>>>> Same problem I had with the pflash device last year...
>>>>>> This break migration :(
>>>>>> What is the best way to do this?
>>>>>
>>>>> Remind me: did we solve the problem with pflash, and if yes, how?
>>>>
>>>> No we can't. The best I could do is add a comment and as this
>>>> is not fixable. See commit aba53a12bd5: ("hw/block/pflash_cfi01:
>>>> Document use of non-CFI compliant command '0x00'").
>>>>
>>>> I now consider the device in maintenance-only
>>>> mode and won't add any new features.
>>>>
>>>> I started working on a new implementation, hoping it can be a
>>>> drop in replacement. Laszlo still has hope that QEMU pflash
>>>> device will support sector locking so firmware developers could
>>>> test upgrading fw in VMs.
>>>>
>>>> Back to the SDcard, it might be less critical, so a migration
>>>> breaking change might be acceptable. I'm only aware of Paolo
>>>> and Kevin using this device for testing. Not sure of its
>>>> importance in production.
>>>
>>> Neither am I.
>>>
>>> Which machine types include this device by default?
>> 
>> To me it looks like it's some of the ARM boards.
>
> My worry is TYPE_PCI_SDHCI ("sdhci-pci"):
>
>     k->vendor_id = PCI_VENDOR_ID_REDHAT;
>     k->device_id = PCI_DEVICE_ID_REDHAT_SDHCI;
>     k->class_id = PCI_CLASS_SYSTEM_SDHCI;
>
> config SDHCI_PCI
>     bool
>     default y if PCI_DEVICES

Ah, now I remember.  Not the first time I wished it wouldn't exist...

>>> How can a non-default device be added, and to which machine types?
>>>
>>> I gather the fix changes device state incompatibly.  Always, or only in
>>> certain states?

I think we need to answer this question.

>>>                  I'm asking because if device state remains compatible
>>> most of the time, we might be able use subsection trickery to keep
>>> migration working most of the time.  Has been done before, I think.