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

[Philippe Mathieu-Daudé]

On 7/17/20 9:18 PM, Havard Skinnemoen wrote:
> On Fri, Jul 17, 2020 at 2:00 AM Philippe Mathieu-Daudé <f4bug@amsat.org> 
> wrote:
>>
>> On 7/17/20 10:27 AM, Philippe Mathieu-Daudé wrote:
>>> On 7/17/20 10:03 AM, Thomas Huth wrote:
>>>> On 17/07/2020 09.48, Philippe Mathieu-Daudé wrote:
>>>>> +Thomas
>>>>
>>>>> On 7/16/20 10:56 PM, Havard Skinnemoen wrote:
>>>>>> On Wed, Jul 15, 2020 at 1:54 PM Havard Skinnemoen
>>>>>> <hskinnemoen@google.com> wrote:
>>>>>>>
>>>>>>> On Wed, Jul 15, 2020 at 3:57 AM Philippe Mathieu-Daudé 
>>>>>>> <f4bug@amsat.org> wrote:
>>>>>>>>
>>>>>>>> On 7/15/20 11:00 AM, Markus Armbruster wrote:
>>>>>>>>> Now my point.  Why first make up user configuration, then use that to
>>>>>>>>> create a BlockBackend, when you could just go ahead and create the
>>>>>>>>> BlockBackend?
>>>>>>>>
>>>>>>>> CLI issue mostly.
>>>>>>>>
>>>>>>>> We can solve it similarly to the recent "sdcard: Do not allow invalid 
>>>>>>>> SD
>>>>>>>> card sizes" patch:
>>>>>>>>
>>>>>>>>  if (!dinfo) {
>>>>>>>>      error_setg(errp, "Missing SPI flash drive");
>>>>>>>>      error_append_hint(errp, "You can use a dummy drive using:\n");
>>>>>>>>      error_append_hint(errp, "-drive if=mtd,driver=null-co,"
>>>>>>>>                              "read-ones=on,size=64M\n);
>>>>>>>>      return;
>>>>>>>>  }
>>>>>>>>
>>>>>>>> having npcm7xx_connect_flash() taking an Error* argument,
>>>>>>>> and MachineClass::init() call it with &error_fatal.
>>>>>>>
>>>>>>> Erroring out if the user specifies a configuration that can't possibly
>>>>>>> boot sounds good to me. Better than trying to come up with defaults
>>>>>>> that are still not going to result in a bootable system.
>>>>>>>
>>>>>>> For testing recovery paths, I think it makes sense to explicitly
>>>>>>> specify a null device as you suggest.
>>>>>>
>>>>>> Hmm, one problem. qom-test fails with
>>>>>>
>>>>>> qemu-system-aarch64: Missing SPI flash drive
>>>>>> You can add a dummy drive using:
>>>>>> -drive if=mtd,driver=null-co,read-zeroes=on,size=32M
>>>>>> Broken pipe
>>>>>> /usr/local/google/home/hskinnemoen/qemu/for-upstream/tests/qtest/libqtest.c:166:
>>>>>> kill_qemu() tried to terminate QEMU process but encountered exit
>>>>>> status 1 (expected 0)
>>>>>> ERROR qom-test - too few tests run (expected 68, got 7)
>>>>>>
>>>>>> So it looks like we might need a different solution to this, unless we
>>>>>> want to make generic tests more machine-aware...
>>>>
>>>> I didn't follow the other mails in this thread, but what we usually do
>>>> in such a case: Add a "if (qtest_enabled())" check to the device or the
>>>> machine to ignore the error if it is running in qtest mode.
>>>
>>> Hmm I'm not sure it works in this case. We could do:
>>>
>>>   if (!dinfo) {
>>>      if (qtest) {
>>>         /* create null drive for qtest */
>>>         opts = ...;
>>>         dinfo = drive_new(opts, IF_MTD, &error_abort);
>>>      } else {
>>>         /* teach user to use proper CLI */
>>>         error_setg(errp, "Missing SPI flash drive");
>>>         error_append_hint(errp, "You can use a dummy drive using:\n");
>>>         error_append_hint(errp, "-drive if=mtd,driver=null-co,"
>>>                                 "read-ones=on,size=64M\n);
>>>      }
>>>   }
>>>
>>> But I'm not sure Markus will enjoy it :)
>>>
>>> Markus, any better idea about how to handle that with automatic qtests?
>>
>> FWIW IDE device has a concept of "Anonymous BlockBackend for an empty
>> drive":
>>
>> static void ide_dev_initfn(IDEDevice *dev, IDEDriveKind kind, Error **errp)
>> {
>>     IDEBus *bus = DO_UPCAST(IDEBus, qbus, dev->qdev.parent_bus);
>>     IDEState *s = bus->ifs + dev->unit;
>>     int ret;
>>
>>     if (!dev->conf.blk) {
>>         if (kind != IDE_CD) {
>>             error_setg(errp, "No drive specified");
>>             return;
>>         } else {
>>             /* Anonymous BlockBackend for an empty drive */
>>             dev->conf.blk = blk_new(qemu_get_aio_context(), 0,
>> BLK_PERM_ALL);
>>             ret = blk_attach_dev(dev->conf.blk, &dev->qdev);
>>             assert(ret == 0);
>>         }
>>     }
> 
> Could someone please remind me what problem we're trying to solve here?

Sorry, out of the scope of your series, which is fine with the current
code base :)

> Currently, if the user (or test) doesn't provide a drive, we pass NULL
> as the block backend to m25p80. This means we'll take the code path in
> m25p_realize() that does
> 
>         trace_m25p80_binding_no_bdrv(s);
>         s->storage = blk_blockalign(NULL, s->size);
>         memset(s->storage, 0xFF, s->size);
> 
> which will look like a freshly chip-erased flash chip.
> 
> Are we looking for a more elegant way to replace those three lines of
> code (+ a couple of conditionals in the writeback paths)?

Yes, I am. Anyway, unrelated to your work, sorry if it confused you.

> 
> But we don't even have a dummy device that looks like an erased flash chip...

No, this is still the design stage, but your series has a quality that
let us foreseen a bit where we are heading...

> 
> Havard
>