Re: [RESEND PATCH v17 5/5] iommu/arm-smmu: Add support for qcom,smmu-v2 variant

[Vivek Gautam]

On 11/24/2018 12:04 AM, Will Deacon wrote:
> On Fri, Nov 23, 2018 at 03:06:29PM +0530, Vivek Gautam wrote:
> > On Fri, Nov 23, 2018 at 2:52 PM Tomasz Figa <tfiga@xxxxxxxxxxxx> wrote:
> > > On Fri, Nov 23, 2018 at 6:13 PM Vivek Gautam
> > > <vivek.gautam@xxxxxxxxxxxxxx> wrote:
> > > > On Wed, Nov 21, 2018 at 11:09 PM Will Deacon <will.deacon@xxxxxxx> wrote:
> > > > > On Fri, Nov 16, 2018 at 04:54:30PM +0530, Vivek Gautam wrote:
> > > > > > @@ -2026,6 +2027,17 @@ ARM_SMMU_MATCH_DATA(arm_mmu401, ARM_SMMU_V1_64K, GENERIC_SMMU);
> > > > > >   ARM_SMMU_MATCH_DATA(arm_mmu500, ARM_SMMU_V2, ARM_MMU500);
> > > > > >   ARM_SMMU_MATCH_DATA(cavium_smmuv2, ARM_SMMU_V2, CAVIUM_SMMUV2);
> > > > > >
> > > > > > +static const char * const qcom_smmuv2_clks[] = {
> > > > > > +     "bus", "iface",
> > > > > > +};
> > > > > > +
> > > > > > +static const struct arm_smmu_match_data qcom_smmuv2 = {
> > > > > > +     .version = ARM_SMMU_V2,
> > > > > > +     .model = QCOM_SMMUV2,
> > > > > > +     .clks = qcom_smmuv2_clks,
> > > > > > +     .num_clks = ARRAY_SIZE(qcom_smmuv2_clks),
> > > > > > +};
> > > > > These seems redundant if we go down the route proposed by Thor, where we
> > > > > just pull all of the clocks out of the device-tree. In which case, why
> > > > > do we need this match_data at all?
> > > > Which is better? Driver relying solely on the device tree to tell
> > > > which all clocks
> > > > are required to be enabled,
> > > > or, the driver deciding itself based on the platform's match data,
> > > > that it should
> > > > have X, Y, & Z clocks that should be supplied from the device tree.
> > > The former would simplify the driver, but would also make it
> > > impossible to spot mistakes in DT, which would ultimately surface out
> > > as very hard to debug bugs (likely complete system lockups).
> > Thanks.
> > Yea, this is how I understand things presently. Relying on device tree
> > puts the things out of driver's control.
> But it also has the undesirable effect of having to update the driver
> code whenever we want to add support for a new SMMU implementation. If
> we do this all in the DT, as Thor is trying to do, then older kernels
> will work well with new hardware.
>
> > Hi Will,
> > Am I unable to understand the intentions here for Thor's clock-fetch
> > design change?
> I'm having trouble parsing your question, sorry. Please work with Thor
> so that we have a single way to get the clock information. My preference
> is to take it from the firmware, for the reason I stated above.
Hi Will,

Sure, thanks. I will work with Thor to get this going.

Hi Thor,
Does it sound okay to you to squash your patch [1] into my patch [2] with
your 'Signed-off-by' tag?
I will update the commit log to include the information about getting
clock details from device tree.

[1] https://patchwork.kernel.org/patch/10628725/
[2] https://patchwork.kernel.org/patch/10686061/

Best regards
Vivek
> Will