Re: [PATCH] coresight: etm4x: fix issues on trcseqevr access

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Wed, Sep 09, 2020 at 10:41:27AM +0100, Mike Leach wrote:
> Hi Mathieu,
> 
> On Tue, 8 Sep 2020 at 18:43, Mathieu Poirier <mathieu.poirier@linaro.org> wrote:
> >
> > Hi Mike,
> >
> > On Mon, 7 Sep 2020 at 10:52, Mike Leach <mike.leach@linaro.org> wrote:
> > >
> > > Hi,
> > >
> > > On Thu, 3 Sep 2020 at 18:42, Mathieu Poirier <mathieu.poirier@linaro.org> wrote:
> > > >
> > > > On Wed, Sep 02, 2020 at 06:37:13PM +0800, Jonathan Zhou wrote:
> > > > > The TRCSEQEVR(3) is reserved, using '@nrseqstate - 1' instead to avoid
> > > > > accessing the reserved register.
> > > > >
> > > > > Fixes: f188b5e76aae ("coresight: etm4x: Save/restore state across CPU low power states")
> > > > > Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> > > > > Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> > > > > Cc: Mike Leach <mike.leach@linaro.org>
> > > > > Cc: Shaokun Zhang <zhangshaokun@hisilicon.com>
> > > > > Cc: lizixian@hisilicon.com
> > > > >
> > > > > Signed-off-by: Jonathan Zhou <jonathan.zhouwen@huawei.com>
> > > > > ---
> > > > >  drivers/hwtracing/coresight/coresight-etm4x.c | 4 ++--
> > > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c
> > > > > index 96425e818fc2..44e44c817bf8 100644
> > > > > --- a/drivers/hwtracing/coresight/coresight-etm4x.c
> > > > > +++ b/drivers/hwtracing/coresight/coresight-etm4x.c
> > > > > @@ -1183,7 +1183,7 @@ static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
> > > > >       state->trcvdsacctlr = readl(drvdata->base + TRCVDSACCTLR);
> > > > >       state->trcvdarcctlr = readl(drvdata->base + TRCVDARCCTLR);
> > > > >
> > > > > -     for (i = 0; i < drvdata->nrseqstate; i++)
> > > > > +     for (i = 0; i < drvdata->nrseqstate - 1; i++)
> > > > >               state->trcseqevr[i] = readl(drvdata->base + TRCSEQEVRn(i));
> > > >
> > > > The section 3.4.3 "Guidelines for trace unit registers to be saved and restored"
> > > > of the ETM4 Architecture Specification (ARM IHI0064F ID042818) is clear on the
> > > > fact that registers TRCSEQEVR0-3 have to be taken into account when saving the
> > >
> > > I think this is a typo in the TRM. I'll ping the docs people in ARM.
> >
> > Did you get an answer from the document people?  Is this really a
> > typographical problem?
> >
> 
> Haven't had a reply, but this is a clear error. All other parts of the
> spec, including programming the device and register descriptions give
> a valid n=0-2 for TRCSEQEVRn.
> TRCSEQEVR3 does not exist, and the assumed location is indeed
> reserved. That said, reserved registers are marked as RES0H - so no
> actual harm can come from reading / writing the register - but we
> should be consistent.
> 
> I would regard section 3.4.3 as a list of registers to save / restore
> as correct with the caveat -  "should they exist in the
> implementation". Quite a few of the register ranges defined in this
> list show the maximum extent of registers where the actual number of
> registers is implementation dependent.

Very well - I will proceed with this patch.

> 
> Thanks
> 
> Mike
> 
> 
> > Thanks,
> > Mathieu
> >
> > >
> > > > trace unit state.
> > > >
> > >
> > > Looking @ the register descriptions for TRCSEQEVRn (7.3.63) in the
> > > above document n=0-2.
> > > The number of states is set by TRCIDR5.NUMSEQSTATE (7.3.35). This can
> > > take the value 0 or 4.
> > > If 4 then there are 3 TRCSEQEVR(n) registers - 0 to 2 - one for each
> > > state transition.
> > >
> > > Thus this patch is correct in using nrseqstate - 1.
> > >
> > > Regards
> > >
> > > Mike
> > >
> > > > Thanks,
> > > > Mathieu
> > > >
> > > > >
> > > > >       state->trcseqrstevr = readl(drvdata->base + TRCSEQRSTEVR);
> > > > > @@ -1288,7 +1288,7 @@ static void etm4_cpu_restore(struct etmv4_drvdata *drvdata)
> > > > >       writel_relaxed(state->trcvdsacctlr, drvdata->base + TRCVDSACCTLR);
> > > > >       writel_relaxed(state->trcvdarcctlr, drvdata->base + TRCVDARCCTLR);
> > > > >
> > > > > -     for (i = 0; i < drvdata->nrseqstate; i++)
> > > > > +     for (i = 0; i < drvdata->nrseqstate - 1; i++)
> > > > >               writel_relaxed(state->trcseqevr[i],
> > > > >                              drvdata->base + TRCSEQEVRn(i));
> > > > > --
> > > > > 1.9.1
> > > > >
> > >
> > >
> > >
> > > --
> > > Mike Leach
> > > Principal Engineer, ARM Ltd.
> > > Manchester Design Centre. UK
> 
> 
> 
> -- 
> Mike Leach
> Principal Engineer, ARM Ltd.
> Manchester Design Centre. UK

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