[edk2-devel] [PATCH v2] ArmPkg/ArmScmiDxe: Fix the calculation of RequiredArraySize in ClockDescribeRates()

[Sudeep Holla]

As per the SCMI specification, section CLOCK_DESCRIBE_RATES mentions
that the value of num_rates_flags[11:0] in the response must be 3 if
the return format is the triplet. Due to the buggy firmware, this was
not noticed for long time. The firmware is now fixed resulting in
ClockDescribeRates() to fail with "Buffer Too Small" error as the
RequiredArraySize gets miscalculated as 72 instead of 24.

Fix the issue by reusing the logic for both the return format which
must work if num_rates_flags has correct value as expected from the
specification.

Cc: Pierre Gondois <Pierre.Gondois at arm.com>
Cc: Girish Pathak <girish.pathak at arm.com>
Cc: Jeff Brasen <jbrasen at nvidia.com>
Reviewed-by: Pierre Gondois <pierre.gondois at arm.com>
Tested-by: Pierre Gondois <pierre.gondois at arm.com>
Reported-by: Sami Mujawar <sami.mujawar at arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla at arm.com>
---
 ArmPkg/Drivers/ArmScmiDxe/ScmiClockProtocol.c | 35 ++++++++-----------
 1 file changed, 14 insertions(+), 21 deletions(-)

v1->v2:
	- Removed the unnecessary and incorrect loop to populate
	  the clock rate triplets(as suggested by Pierre)

Note the real delta is just 7 lines deletion when viewed with ignored
spacechanges.

diff --git a/ArmPkg/Drivers/ArmScmiDxe/ScmiClockProtocol.c b/ArmPkg/Drivers/ArmScmiDxe/ScmiClockProtocol.c
index 12a7e6df5d43..f092208a6601 100644
--- a/ArmPkg/Drivers/ArmScmiDxe/ScmiClockProtocol.c
+++ b/ArmPkg/Drivers/ArmScmiDxe/ScmiClockProtocol.c
@@ -236,12 +236,7 @@ ClockDescribeRates (
       *TotalRates = NUM_RATES (DescribeRates->NumRatesFlags)
                     + NUM_REMAIN_RATES (DescribeRates->NumRatesFlags);
 
-      if (*Format == ScmiClockRateFormatDiscrete) {
-        RequiredArraySize = (*TotalRates) * sizeof (UINT64);
-      } else {
-        // We need to return triplet of 64 bit value for each rate
-        RequiredArraySize = (*TotalRates) * 3 * sizeof (UINT64);
-      }
+      RequiredArraySize = (*TotalRates) * sizeof (UINT64);
 
       if (RequiredArraySize > (*RateArraySize)) {
         *RateArraySize = RequiredArraySize;
@@ -259,23 +254,21 @@ ClockDescribeRates (
           ConvertTo64Bit (Rate->Low, Rate->High);
       }
     } else {
-      for (RateNo = 0; RateNo < NUM_RATES (DescribeRates->NumRatesFlags); RateNo++) {
-        // Linear clock rates from minimum to maximum in steps
-        // Minimum clock rate.
-        Rate                                    = &DescribeRates->Rates[RateOffset++];
-        RateArray[RateIndex].ContinuousRate.Min =
-          ConvertTo64Bit (Rate->Low, Rate->High);
+      // Linear clock rates from minimum to maximum in steps
+      // Minimum clock rate.
+      Rate                                    = &DescribeRates->Rates[RateOffset++];
+      RateArray[RateIndex].ContinuousRate.Min =
+        ConvertTo64Bit (Rate->Low, Rate->High);
 
-        Rate = &DescribeRates->Rates[RateOffset++];
-        // Maximum clock rate.
-        RateArray[RateIndex].ContinuousRate.Max =
-          ConvertTo64Bit (Rate->Low, Rate->High);
+      Rate = &DescribeRates->Rates[RateOffset++];
+      // Maximum clock rate.
+      RateArray[RateIndex].ContinuousRate.Max =
+        ConvertTo64Bit (Rate->Low, Rate->High);
 
-        Rate = &DescribeRates->Rates[RateOffset++];
-        // Step.
-        RateArray[RateIndex++].ContinuousRate.Step =
-          ConvertTo64Bit (Rate->Low, Rate->High);
-      }
+      Rate = &DescribeRates->Rates[RateOffset++];
+      // Step.
+      RateArray[RateIndex++].ContinuousRate.Step =
+        ConvertTo64Bit (Rate->Low, Rate->High);
     }
   } while (NUM_REMAIN_RATES (DescribeRates->NumRatesFlags) != 0);
 
-- 
2.39.1



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