On 3/11/2021 1:00 AM, Loic Poulain wrote:
Hi Bhaumik,
On Thu, 11 Mar 2021 at 00:31, Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx> wrote:
Introduce helper function to allow MHI core driver to poll for
a value in a register field. This helps reach a common path to
read and poll register values along with a retry time interval.
Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
---
drivers/bus/mhi/core/internal.h | 3 +++
drivers/bus/mhi/core/main.c | 23 +++++++++++++++++++++++
2 files changed, 26 insertions(+)
diff --git a/drivers/bus/mhi/core/internal.h b/drivers/bus/mhi/core/internal.h
index 6f80ec3..005286b 100644
--- a/drivers/bus/mhi/core/internal.h
+++ b/drivers/bus/mhi/core/internal.h
@@ -643,6 +643,9 @@ int __must_check mhi_read_reg(struct mhi_controller *mhi_cntrl,
int __must_check mhi_read_reg_field(struct mhi_controller *mhi_cntrl,
void __iomem *base, u32 offset, u32 mask,
u32 shift, u32 *out);
+int __must_check mhi_poll_reg_field(struct mhi_controller *mhi_cntrl,
+ void __iomem *base, u32 offset, u32 mask,
+ u32 shift, u32 val, u32 delayus);
void mhi_write_reg(struct mhi_controller *mhi_cntrl, void __iomem *base,
u32 offset, u32 val);
void mhi_write_reg_field(struct mhi_controller *mhi_cntrl, void __iomem *base,
diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
index 4e0131b..7c7f41a 100644
--- a/drivers/bus/mhi/core/main.c
+++ b/drivers/bus/mhi/core/main.c
@@ -4,6 +4,7 @@
*
*/
+#include <linux/delay.h>
#include <linux/device.h>
#include <linux/dma-direction.h>
#include <linux/dma-mapping.h>
@@ -37,6 +38,28 @@ int __must_check mhi_read_reg_field(struct mhi_controller *mhi_cntrl,
return 0;
}
+int __must_check mhi_poll_reg_field(struct mhi_controller *mhi_cntrl,
+ void __iomem *base, u32 offset,
+ u32 mask, u32 shift, u32 val, u32 delayus)
+{
+ int ret;
+ u32 out, retry = (mhi_cntrl->timeout_ms * 1000) / delayus;
+
+ while (retry--) {
+ ret = mhi_read_reg_field(mhi_cntrl, base, offset, mask, shift,
+ &out);
+ if (ret)
+ return ret;
+
+ if (out == val)
+ return 0;
+
+ udelay(delayus);
Have you read my previous comment?
Do you really want to risk hogging the CPU for several seconds? we
know that some devices take several seconds to start/boot.
Why not using msleep variant here?
usleep_range() if there is a desire to stay in us units?
Given that the use of this function is for 25ms in one case, I wonder if
this warning is applicable:
https://elixir.bootlin.com/linux/latest/source/include/linux/delay.h#L28
Counter point, 1ms latency over PCIe is not unusual. I know we've
removed the PCIe dependencies from MHI, but PCIe is the real usecase at
this time. Seems like this function could behave a bit weird if the
parameter to udelay is something like "100", but the
mhi_read_reg_field() call takes significantly longer than that. Feels
like in some scenarios, we could actually exceed the timeout by a
non-trivial margin.
I guess I'm going back and forth in determining if us scale timing is a
benefit in any way.
--
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.
