[PATCH v2 2/3] lib: utils/timer: mtimer: add a quirk for lacking mtime register

[Icenowy Zheng]

T-Head developers surely have a different understanding of time CSR and
CLINT's mtime register with SiFive ones, that they did not implement
the mtime register at all -- as shown in openC906 source code, their
time CSR value is just exposed at the top of their processor IP block
and expects an external continous counter, which makes it not
overrideable, and thus mtime register is not implemented, even not for
reading. However, if CLINTEE is not enabled in T-Head's MXSTATUS
extended CSR, these systems still rely on the mtimecmp registers to
generate timer interrupts. This makes it necessary to implement T-Head
C9xx CLINT support in OpenSBI MTIMER driver, which skips implementing
reading mtime register and falls back to default code that reads time
CSR.

Add a quirk into MTIMER driver, which represents a mtime register is
lacking and time CSR value should be used instead.

Signed-off-by: Icenowy Zheng <uwu at icenowy.me>
---
Changes in v2:
- Dropped has_mtime field in aclint_mtimer_data, use mtime_size = 0
  (which is disallowed before) to mark absence of mtime.
- Dropped the code that specially handle the existence of mtime when
  registering memory ranges -- the function will just be a no-op when
  size is 0.

 lib/utils/timer/aclint_mtimer.c    | 11 ++++++++---
 lib/utils/timer/fdt_timer_mtimer.c | 30 ++++++++++++++++++++----------
 2 files changed, 28 insertions(+), 13 deletions(-)

diff --git a/lib/utils/timer/aclint_mtimer.c b/lib/utils/timer/aclint_mtimer.c
index 3f00c21..1846a9a 100644
--- a/lib/utils/timer/aclint_mtimer.c
+++ b/lib/utils/timer/aclint_mtimer.c
@@ -149,10 +149,10 @@ int aclint_mtimer_cold_init(struct aclint_mtimer_data *mt,
 	int rc;
 
 	/* Sanity checks */
-	if (!mt || !mt->mtime_size ||
+	if (!mt ||
 	    (mt->hart_count && !mt->mtimecmp_size) ||
-	    (mt->mtime_addr & (ACLINT_MTIMER_ALIGN - 1)) ||
-	    (mt->mtime_size & (ACLINT_MTIMER_ALIGN - 1)) ||
+	    (mt->mtime_size && (mt->mtime_addr & (ACLINT_MTIMER_ALIGN - 1))) ||
+	    (mt->mtime_size && (mt->mtime_size & (ACLINT_MTIMER_ALIGN - 1))) ||
 	    (mt->mtimecmp_addr & (ACLINT_MTIMER_ALIGN - 1)) ||
 	    (mt->mtimecmp_size & (ACLINT_MTIMER_ALIGN - 1)) ||
 	    (mt->first_hartid >= SBI_HARTMASK_MAX_BITS) ||
@@ -178,6 +178,11 @@ int aclint_mtimer_cold_init(struct aclint_mtimer_data *mt,
 	for (i = 0; i < mt->hart_count; i++)
 		mtimer_hartid2data[mt->first_hartid + i] = mt;
 
+	if (!mt->mtime_size) {
+		/* Disable reading mtime when mtime is not available */
+		mtimer.timer_value = NULL;
+	}
+
 	/* Add MTIMER regions to the root domain */
 	if (mt->mtime_addr == (mt->mtimecmp_addr + mt->mtimecmp_size)) {
 		rc = sbi_domain_root_add_memrange(mt->mtimecmp_addr,
diff --git a/lib/utils/timer/fdt_timer_mtimer.c b/lib/utils/timer/fdt_timer_mtimer.c
index 7b8546b..a0adc70 100644
--- a/lib/utils/timer/fdt_timer_mtimer.c
+++ b/lib/utils/timer/fdt_timer_mtimer.c
@@ -18,6 +18,7 @@
 struct timer_mtimer_quirks {
 	unsigned int	mtime_offset;
 	bool		has_64bit_mmio;
+	bool		without_mtime;
 };
 
 static unsigned long mtimer_count = 0;
@@ -53,12 +54,16 @@ static int timer_mtimer_cold_init(void *fdt, int nodeoff,
 		/* Set CLINT addresses */
 		mt->mtimecmp_addr = addr[0] + ACLINT_DEFAULT_MTIMECMP_OFFSET;
 		mt->mtimecmp_size = ACLINT_DEFAULT_MTIMECMP_SIZE;
-		mt->mtime_addr = addr[0] + ACLINT_DEFAULT_MTIME_OFFSET;
-		mt->mtime_size = size[0] - mt->mtimecmp_size;
-		/* Adjust MTIMER address and size for CLINT device */
-		mt->mtime_addr += quirks->mtime_offset;
+		if (!quirks->without_mtime) {
+			mt->mtime_addr = addr[0] + ACLINT_DEFAULT_MTIME_OFFSET;
+			mt->mtime_size = size[0] - mt->mtimecmp_size;
+			/* Adjust MTIMER address and size for CLINT device */
+			mt->mtime_addr += quirks->mtime_offset;
+			mt->mtime_size -= quirks->mtime_offset;
+		} else {
+			mt->mtime_addr = mt->mtime_size = 0;
+		}
 		mt->mtimecmp_addr += quirks->mtime_offset;
-		mt->mtime_size -= quirks->mtime_offset;
 		/* Apply additional CLINT quirks */
 		mt->has_64bit_mmio = quirks->has_64bit_mmio;
 	} else { /* RISC-V ACLINT MTIMER */
@@ -70,12 +75,17 @@ static int timer_mtimer_cold_init(void *fdt, int nodeoff,
 	}
 
 	/* Check if MTIMER device has shared MTIME address */
-	mt->has_shared_mtime = false;
-	for (i = 0; i < mtimer_count; i++) {
-		if (mtimer[i].mtime_addr == mt->mtime_addr) {
-			mt->has_shared_mtime = true;
-			break;
+	if (mt->mtime_size) {
+		mt->has_shared_mtime = false;
+		for (i = 0; i < mtimer_count; i++) {
+			if (mtimer[i].mtime_addr == mt->mtime_addr) {
+				mt->has_shared_mtime = true;
+				break;
+			}
 		}
+	} else {
+		/* Assume shared time CSR */
+		mt->has_shared_mtime = true;
 	}
 
 	/* Initialize the MTIMER device */
-- 
2.38.1