Provide option to support AMOs only on I/O, not DTIM/D$

src/main/scala/rocket/DCache.scala

@@ -76,7 +76,7 @@ class DCacheModule(outer: DCache) extends HellaCacheModule(outer) {
   val eccBits = eccBytes * 8
   require(isPow2(eccBytes) && eccBytes <= wordBytes)
   require(eccBytes == 1 || !dECC.isInstanceOf[IdentityCode])
-  val usingRMW = eccBytes > 1 || usingAtomics
+  val usingRMW = eccBytes > 1 || usingAtomicsInCache
 
   // tags
   val replacer = cacheParams.replacement
@@ -688,11 +688,11 @@ class DCacheModule(outer: DCache) extends HellaCacheModule(outer) {
   if (usingRMW) {
     val amoalu = Module(new AMOALU(xLen))
     amoalu.io.mask := pstore1_mask
-    amoalu.io.cmd := (if (usingAtomics) pstore1_cmd else M_XWR)
+    amoalu.io.cmd := (if (usingAtomicsInCache) pstore1_cmd else M_XWR)
     amoalu.io.lhs := s2_data_word
     amoalu.io.rhs := pstore1_data
     pstore1_storegen_data := amoalu.io.out
-  } else {
+  } else if (!usingAtomics) {
     assert(!(s1_valid_masked && s1_read && s1_write), "unsupported D$ operation")
   }
   when (s2_correct) { pstore1_storegen_data := s2_data_word_corrected }

src/main/scala/rocket/RocketCore.scala

@@ -18,6 +18,7 @@ case class RocketCoreParams(
   useUser: Boolean = false,
   useDebug: Boolean = true,
   useAtomics: Boolean = true,
+  useAtomicsOnlyForIO: Boolean = false,
   useCompressed: Boolean = true,
   nLocalInterrupts: Int = 0,
   nBreakpoints: Int = 1,

src/main/scala/rocket/ScratchpadSlavePort.scala

@@ -100,7 +100,7 @@ trait CanHaveScratchpad extends HasHellaCache with HasICacheFrontend {
   val cacheBlockBytes = p(CacheBlockBytes)
 
   val scratch = tileParams.dcache.flatMap { d => d.scratch.map(s =>
-    LazyModule(new ScratchpadSlavePort(AddressSet(s, d.dataScratchpadBytes-1), xBytes, tileParams.core.useAtomics)))
+    LazyModule(new ScratchpadSlavePort(AddressSet(s, d.dataScratchpadBytes-1), xBytes, tileParams.core.useAtomics && !tileParams.core.useAtomicsOnlyForIO)))
   }
 
   val intOutputNode = tileParams.core.tileControlAddr.map(dummy => IntIdentityNode())

src/main/scala/rocket/TLB.scala

@@ -117,8 +117,8 @@ class TLB(instruction: Boolean, lgMaxSize: Int, nEntries: Int)(implicit edge: TL
   val homogeneous = TLBPageLookup(edge.manager.managers, xLen, p(CacheBlockBytes), BigInt(1) << pgIdxBits)(mpu_physaddr).homogeneous
   val prot_r = fastCheck(_.supportsGet) && pmp.io.r
   val prot_w = fastCheck(_.supportsPutFull) && pmp.io.w
-  val prot_al = fastCheck(_.supportsLogical) || cacheable
-  val prot_aa = fastCheck(_.supportsArithmetic) || cacheable
+  val prot_al = fastCheck(_.supportsLogical) || (cacheable && usingAtomicsInCache)
+  val prot_aa = fastCheck(_.supportsArithmetic) || (cacheable && usingAtomicsInCache)
   val prot_x = fastCheck(_.executable) && pmp.io.x
   val prot_eff = fastCheck(Seq(RegionType.PUT_EFFECTS, RegionType.GET_EFFECTS) contains _.regionType)
 
@@ -190,7 +190,7 @@ class TLB(instruction: Boolean, lgMaxSize: Int, nEntries: Int)(implicit edge: TL
     (if (vpnBits == vpnBitsExtended) Bool(false)
      else (io.req.bits.vaddr.asSInt < 0.S) =/= (vpn.asSInt < 0.S))
 
-  val lrscAllowed = Mux(Bool(usingDataScratchpad), 0.U, c_array)
+  val lrscAllowed = Mux(Bool(usingDataScratchpad || usingAtomicsOnlyForIO), 0.U, c_array)
   val ae_array =
     Mux(misaligned, eff_array, 0.U) |
     Mux(Bool(usingAtomics) && io.req.bits.cmd.isOneOf(M_XLR, M_XSC), ~lrscAllowed, 0.U)

src/main/scala/tile/Core.scala

@@ -17,6 +17,7 @@ trait CoreParams {
   val useUser: Boolean
   val useDebug: Boolean
   val useAtomics: Boolean
+  val useAtomicsOnlyForIO: Boolean
   val useCompressed: Boolean
   val mulDiv: Option[MulDivParams]
   val fpu: Option[FPUParams]
@@ -47,6 +48,8 @@ trait HasCoreParameters extends HasTileParameters {
   val usingMulDiv = coreParams.mulDiv.nonEmpty
   val usingFPU = coreParams.fpu.nonEmpty
   val usingAtomics = coreParams.useAtomics
+  val usingAtomicsOnlyForIO = coreParams.useAtomicsOnlyForIO
+  val usingAtomicsInCache = usingAtomics && !usingAtomicsOnlyForIO
   val usingCompressed = coreParams.useCompressed
 
   val retireWidth = coreParams.retireWidth