Reading the register (if allowed) after writing is to ensure writing
is completed on a posted bus. The endianness of reading doesn't matter.
Signed-off-by: York Sun <yorksun@xxxxxxxxxxxxx>
---
drivers/i2c/muxes/i2c-mux-reg.c | 28 ++++++++++++++--------------
1 file changed, 14 insertions(+), 14 deletions(-)
diff --git a/drivers/i2c/muxes/i2c-mux-reg.c b/drivers/i2c/muxes/i2c-mux-reg.c
index 86d41d36..7f2a1ae 100644
--- a/drivers/i2c/muxes/i2c-mux-reg.c
+++ b/drivers/i2c/muxes/i2c-mux-reg.c
@@ -31,28 +31,28 @@ static int i2c_mux_reg_set(const struct regmux *mux, unsigned int chan_id)
if (!mux->data.reg)
return -EINVAL;
+ /*
+ * Write to the register, followed by a read to ensure the write is
+ * completed on a "posted" bus, for example PCI or write buffers.
+ * The endianness of reading doesn't matter and the return data
+ * is not used.
+ */
switch (mux->data.reg_size) {
case 4:
- if (mux->data.little_endian) {
+ if (mux->data.little_endian)
iowrite32(chan_id, mux->data.reg);
- if (!mux->data.write_only)
- ioread32(mux->data.reg);
- } else {
+ else
iowrite32be(chan_id, mux->data.reg);
- if (!mux->data.write_only)
- ioread32(mux->data.reg);
- }
+ if (!mux->data.write_only)
+ ioread32(mux->data.reg);
break;
case 2:
- if (mux->data.little_endian) {
+ if (mux->data.little_endian)
iowrite16(chan_id, mux->data.reg);
- if (!mux->data.write_only)
- ioread16(mux->data.reg);
- } else {
+ else
iowrite16be(chan_id, mux->data.reg);
- if (!mux->data.write_only)
- ioread16be(mux->data.reg);
- }
+ if (!mux->data.write_only)
+ ioread16(mux->data.reg);
break;
case 1:
iowrite8(chan_id, mux->data.reg);
--
1.7.9.5
--
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