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Error grants (#1025)

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* CacheCork: an error Grant still says 'toT' even though it is transient

Grants with errors must be handled by a client as though no actual
permissions were obtained, so that two clients do not both end up believing
that they own a block which is only temporarily offline. However, the
Grant MESSAGE should still match the request; ie. if you did Acquire.NtoT,
the response must be Grant.toT, even though the 'error' bit signals that
the Grant actually grants no permissions.

This keeps the implementation of request-response tracking in interstitial
adapters and FSMs simple, consistent with the way multibeat errors must
include all their beats.

* Error: handle permissions properly
This commit is contained in:
Wesley W. Terpstra
2017-10-02 14:49:25 -07:00
committed by GitHub
parent 723af5e6b6
commit a2dc13669a
2 changed files with 3 additions and 6 deletions
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5
src/main/scala/tilelink/CacheCork.scala
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@ -100,10 +100,7 @@ class TLCacheCork(unsafe: Boolean = false)(implicit p: Parameters) extends LazyM
when (out.d.bits.opcode === AccessAckData && out.d.bits.source(0)) {
d_d.bits.opcode := GrantData
// On Grant error, you do NOT get the permissions you asked for.
// We only enter this case from NtoT or NtoB, so that means use toN.
// (the BtoT case was handled by a_d)
d_d.bits.param := Mux(out.d.bits.error, TLPermissions.toN, TLPermissions.toT)
d_d.bits.param := TLPermissions.toT
}
when (out.d.bits.opcode === AccessAck && !out.d.bits.source(0)) {
d_d.bits.opcode := ReleaseAck