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

Hi Thor,


On 11/26/2018 8:11 PM, Thor Thayer wrote:

Hi Vivek,

On 11/26/18 4:55 AM, Vivek Gautam wrote:

quoted

On 11/24/2018 12:04 AM, Will Deacon wrote:

quoted

On Fri, Nov 23, 2018 at 03:06:29PM +0530, Vivek Gautam wrote:

quoted

On Fri, Nov 23, 2018 at 2:52 PM Tomasz Figa [off-list ref] 
wrote:

quoted

On Fri, Nov 23, 2018 at 6:13 PM Vivek Gautam
[off-list ref] wrote:

quoted

On Wed, Nov 21, 2018 at 11:09 PM Will Deacon 
[off-list ref] wrote:

quoted

On Fri, Nov 16, 2018 at 04:54:30PM +0530, Vivek Gautam wrote:

quoted

@@ -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.

quoted

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/

Yes, that would be great and easier to understand than my patch on top 
of yours.

Additionally, can you remove the "Error:" as Will requested as part of 
the squash?

Thanks for your consent. I have reworked the patch today, and have 
addressed Will's
comment. I will give a try on the board and post it by tomorrow.

Best regards
Vivek

Thank you!

Thor

quoted

Best regards
Vivek

quoted

Will

_______________________________________________
Freedreno mailing list
Freedreno@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/freedreno