diff mbox series

[PULL,7/7] hw/nvram: Avoid unnecessary Xilinx eFuse backstore write

Message ID 20230717124746.759085-8-peter.maydell@linaro.org
State Accepted
Commit c2c1c4a35c7c2b1a4140b0942b9797c857e476a4
Headers show
Series [PULL,1/7] hw/arm/sbsa-ref: set 'slots' property of xhci | expand

Commit Message

Peter Maydell July 17, 2023, 12:47 p.m. UTC 
From: Tong Ho <tong.ho@amd.com>

Add a check in the bit-set operation to write the backstore
only if the affected bit is 0 before.

With this in place, there will be no need for callers to
do the checking in order to avoid unnecessary writes.

Signed-off-by: Tong Ho <tong.ho@amd.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 hw/nvram/xlnx-efuse.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/hw/nvram/xlnx-efuse.c b/hw/nvram/xlnx-efuse.c
index fdfffaab99c..655c40b8d1e 100644
--- a/hw/nvram/xlnx-efuse.c
+++ b/hw/nvram/xlnx-efuse.c
@@ -143,6 +143,8 @@  static bool efuse_ro_bits_find(XlnxEFuse *s, uint32_t k)
 
 bool xlnx_efuse_set_bit(XlnxEFuse *s, unsigned int bit)
 {
+    uint32_t set, *row;
+
     if (efuse_ro_bits_find(s, bit)) {
         g_autofree char *path = object_get_canonical_path(OBJECT(s));
 
@@ -152,8 +154,13 @@  bool xlnx_efuse_set_bit(XlnxEFuse *s, unsigned int bit)
         return false;
     }
 
-    s->fuse32[bit / 32] |= 1 << (bit % 32);
-    efuse_bdrv_sync(s, bit);
+    /* Avoid back-end write unless there is a real update */
+    row = &s->fuse32[bit / 32];
+    set = 1 << (bit % 32);
+    if (!(set & *row)) {
+        *row |= set;
+        efuse_bdrv_sync(s, bit);
+    }
     return true;
 }