On Fri, Jun 15, 2018 at 10:15:54AM +0200, Corentin Labbe wrote:
> On Fri, Jun 15, 2018 at 09:57:54AM +0200, Maxime Ripard wrote:
> > On Thu, Jun 14, 2018 at 09:36:59PM +0200, Corentin Labbe wrote:
> > > Running a qemu emulated cubieboard with sun4i-ss driver enabled led to a never
> > > ending boot.
> > > This is due to sun4i-ss deadlocked and taking all cpu in an infinite loop.
> > > Since the crypto hardware is not implemented, all registers are read as 0.
> > > So sun4i-ss will never progress in any operations. (TX_CNT being always 0)
> > >
> > > The first idea is to add a "TX_CNT always zero timeout" but this made cipher/hash loops
> > > more complex and prevent a case that never happen on real hardware.
> > >
> > > The best way to fix is to check at probe time if we run on a virtual
> > > machine with hardware emulated but non-implemented and prevent
> > > sun4i-ss to be loaded in that case.
> > > Letting sun4i-ss to load is useless anyway since all crypto algorithm will be
> > > disabled since they will fail crypto selftests.
> > >
> > > Tested-on: qemu-cubieboard
> > > Tested-on: cubieboard2
> > >
> > > Signed-off-by: Corentin Labbe <clabbe.montjoie@xxxxxxxxx>
> > > ---
> > > drivers/crypto/sunxi-ss/sun4i-ss-core.c | 10 ++++++++++
> > > 1 file changed, 10 insertions(+)
> > >
> > > diff --git a/drivers/crypto/sunxi-ss/sun4i-ss-core.c b/drivers/crypto/sunxi-ss/sun4i-ss-core.c
> > > index a81d89b3b7d8..a178e80adcf3 100644
> > > --- a/drivers/crypto/sunxi-ss/sun4i-ss-core.c
> > > +++ b/drivers/crypto/sunxi-ss/sun4i-ss-core.c
> > > @@ -341,9 +341,18 @@ static int sun4i_ss_probe(struct platform_device *pdev)
> > > * I expect to be a sort of Security System Revision number.
> > > * Since the A80 seems to have an other version of SS
> > > * this info could be useful
> > > + * Detect virtual machine with non-implemented hardware
> > > + * (qemu-cubieboard) by checking the register value after a write to it.
> > > + * On non-implemented hardware, all registers are read as 0.
> > > + * On real hardware we should have a value > 0.
> > > */
> > > writel(SS_ENABLED, ss->base + SS_CTL);
> > > v = readl(ss->base + SS_CTL);
> > > + if (!v) {
> > > + dev_err(&pdev->dev, "Qemu with non-implemented SS detected.\n");
> > > + err = -ENODEV;
> > > + goto error_rst;
> > > + }
> >
> > This is wrong way to tackle the issue. There's multiple reason why
> > this could happen (for example the device not being clocked, or
> > maintained in reset). There's nothing specific about qemu here, and
> > the fundamental issue isn't that the device isn't functional in qemu,
> > it's that qemu lies about which hardware it can emulate in the DT it
> > passes to the kernel.
> >
> > There's no way this can scale, alone from the fact that qemu should
> > patch the DT according to what it can do. Not trying to chase after
> > each and every device that is broken in qemu.
> >
> > NAK.
> >
>
> My fix detect also when the device is badly clocked.
In which case, the proper fix is to enable the clock, not throw the
kernel's arm up in the air.
Maxime
--
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com
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