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

[Havard Skinnemoen]

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?

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)?

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

Havard