Re: [PATCH v9 4/5] iommu/arm-smmu: add ACTLR data and support for SM8550

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On 2/21/2024 6:51 PM, Will Deacon wrote:
On Wed, Feb 21, 2024 at 02:25:26PM +0530, Bibek Kumar Patro wrote:
On 2/13/2024 7:17 PM, Will Deacon wrote:
On Tue, Jan 23, 2024 at 08:15:42PM +0530, Bibek Kumar Patro wrote:
Add ACTLR data table for SM8550 along with support for
same including SM8550 specific implementation operations.

Signed-off-by: Bibek Kumar Patro <quic_bibekkum@xxxxxxxxxxx>
   drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 90 ++++++++++++++++++++++
   1 file changed, 90 insertions(+)

diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
index 6004c6d9a7b2..db15b1eade97 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
@@ -23,6 +23,86 @@

   #define CPRE			(1 << 1)
   #define CMTLB			(1 << 0)
+#define PREFETCH_SHIFT		8
+#define PREFETCH_SWITCH_GFX	(5 << 3)
+static const struct actlr_config sm8550_apps_actlr_cfg[] = {
+	{ 0x18a0, 0x0000, PREFETCH_SHALLOW | CPRE | CMTLB },
+	{ 0x18e0, 0x0000, PREFETCH_SHALLOW | CPRE | CMTLB },
+	{ 0x0800, 0x0020, PREFETCH_DEFAULT | CMTLB },
+	{ 0x1800, 0x00c0, PREFETCH_DEFAULT | CMTLB },
+	{ 0x1820, 0x0000, PREFETCH_DEFAULT | CMTLB },
+	{ 0x1860, 0x0000, PREFETCH_DEFAULT | CMTLB },
+	{ 0x0c01, 0x0020, PREFETCH_DEEP | CPRE | CMTLB },
+	{ 0x0c02, 0x0020, PREFETCH_DEEP | CPRE | CMTLB },
+	{ 0x0c03, 0x0020, PREFETCH_DEEP | CPRE | CMTLB },
+	{ 0x0c04, 0x0020, PREFETCH_DEEP | CPRE | CMTLB },
+	{ 0x0c05, 0x0020, PREFETCH_DEEP | CPRE | CMTLB },
+	{ 0x0c06, 0x0020, PREFETCH_DEEP | CPRE | CMTLB },


Isn't this effectively hard-coding the topology of the SoC in the driver?
Wouldn't it better describing higher-level prefetch properties in the DT
nodes corresponding to the upstream devices?

Since prefetch data stored in this table represent settings for the
ACTLR register, and doesn't exactly define the hardware (So in this
manner prefetch data won't exactly be a part of soc topology ?).

The first two columns of the table are StreamID/Mask pairs, no? How is that
_not_ the SoC topology? I really think it would be better to define some
high-level prefetch properties in the DT binding which can be put on the
master nodes.

So it seemed apt not to use the device tree for storing the prefetch
property. Hence we reverted from the DT approach (initial proposal in
RFC to piggyback on iommus property to store prefetch settings) back to use
driver for storing this data.

Some drivers use the same approach for storing their platform specific
data. Examples being
These drivers were taken as reference for storing platform specific ACTLR

I don't know anything about those drivers, but on the SMMU side we already
have ways to describe the topology in the DT and the driver is using them,
so I'm struggling to see the need to add these tables as well.

But as I said before, if Robin and the DT folks prefer this approach,
then I won't get in the way.

With the driver approach at the current state of patches, it has been ACKed by DT folks and it seems there has been no concern/objection from Robin till now.
So can this patch go ahead Will?
Let us know Robin of your opinion as well please.

Thanks & regards,


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