On Fri, Sep 27, 2013 at 05:51:57AM -0400, Will Deacon wrote:
> Hi Andreas,
>
> On Thu, Sep 26, 2013 at 11:36:14PM +0100, Andreas Herrmann wrote:
> > Currently it is derived from smmu resource size. In case of a
> > mismatchin between the two calculations trust DT more than register
> > values and overwrite cb_base.
>
> I thought the driver already favoured the DT?
>
> > @@ -1702,12 +1704,23 @@ static int arm_smmu_device_cfg_probe(struct
> > arm_smmu_device *smmu)
> >
> > /* Check that we ioremapped enough */
> > size = 1 << (((id >> ID1_NUMPAGENDXB_SHIFT) & ID1_NUMPAGENDXB_MASK) +
> > 1);
> > - size *= (smmu->pagesize << 1);
> > + size *= smmu->pagesize;
> > + smmu->cb_base = smmu->base + size;
> > + size *= 2;
> > +
> > if (smmu->size < size)
> > dev_warn(smmu->dev,
> > "device is 0x%lx bytes but only mapped 0x%lx!\n",
> > size, smmu->size);
> >
> > + t = (unsigned long) smmu->base + (smmu->size >> 1);
> > + if ((unsigned long)smmu->cb_base != t) {
> > + dev_warn(smmu->dev, "address space mismatch, "
> > + "overwriting cb_base (old: 0x%lx, new: 0x%lx)\n",
> > + (unsigned long) smmu->cb_base, t);
> > + smmu->cb_base = (void *) t;
> > + }
> > +
>
> I expect I'm just being slow here (only one coffee in), but I can't see what
> this gets us over the current use of resource_size (which goes and uses the
> DT).
On balance it adds a warning if there is an inconsistency between the
resource size and the relevant registers describing the SMMU address
space.
If there is no such warning you might use a broken DT (with wrong
resource size) causing weird malfunction (because cb_base might be
wrong) and it will take some effort to root cause this.
But if you see such a warning it's clear what to check first.
I admit the commit message is misleading (somehow inherited from the
previous patch version) and maybe this kind of consistency check
should not be combined with cb_base calculation but moved into a
separate function called from arm_smmu_device_cfg_probe.
Andreas
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