Re: [PATCH v3 9/9] bus: mhi: ep: wake up host is the MHI state is in M3

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On 7/7/2023 8:42 PM, Bjorn Helgaas wrote:
On Fri, Jul 07, 2023 at 02:41:57PM +0300, Dan Carpenter wrote:
On Fri, Jul 07, 2023 at 04:33:56PM +0530, Krishna chaitanya chundru wrote:
If the MHI state is in M3 then the most probably the host kept the
device in D3 hot or D3 cold, due to that endpoint transctions will not
be read by the host, so endpoint wakes up host to bring the host to D0
which eventually bring back the MHI state to M0.

Signed-off-by: Krishna chaitanya chundru <quic_krichai@xxxxxxxxxxx>
  drivers/bus/mhi/ep/main.c | 28 ++++++++++++++++++++++++++++
  1 file changed, 28 insertions(+)

diff --git a/drivers/bus/mhi/ep/main.c b/drivers/bus/mhi/ep/main.c
index 6008818..46a8a3c 100644
--- a/drivers/bus/mhi/ep/main.c
+++ b/drivers/bus/mhi/ep/main.c
@@ -25,6 +25,27 @@ static DEFINE_IDA(mhi_ep_cntrl_ida);
  static int mhi_ep_create_device(struct mhi_ep_cntrl *mhi_cntrl, u32 ch_id);
  static int mhi_ep_destroy_device(struct device *dev, void *data);
+static bool mhi_ep_wake_host(struct mhi_ep_cntrl *mhi_cntrl)
+	enum mhi_state state;
+	bool mhi_reset;
+	u32 count = 0;
+	mhi_cntrl->wakeup_host(mhi_cntrl);
+	/* Wait for Host to set the M0 state */
+	do {
+		msleep(M0_WAIT_DELAY_MS);
+		mhi_ep_mmio_get_mhi_state(mhi_cntrl, &state, &mhi_reset);
+		count++;
+	} while (state != MHI_STATE_M0 && count < M0_WAIT_COUNT);
+	if (state != MHI_STATE_M0)
+		return false;
Functions which return false on success are an abomination.  Also
boolean functions should be named for the question they answer such
as access_ok() or has_feature() etc.
+1.  Also nice if boolean functions do not have side effects, so in
this case, where mhi_ep_wake_host() *does* something that might fail,
I think "return 0 for success or negative error value" is easier to

sure Dan and Bjorn I will replace bool with int return type as suggested in the next patch series.

- KC

Write it like this:

static int mhi_ep_wake_host(struct mhi_ep_cntrl *mhi_cntrl)
	enum mhi_state state;
	bool mhi_reset;
	int count = 0;


	while (count++ < M0_WAIT_COUNT) {

		mhi_ep_mmio_get_mhi_state(mhi_cntrl, &state, &mhi_reset);
		if (state == MHI_STATE_M0)
			return 0;
	return -ENODEV;

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