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

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

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.

Actually, I think it's the caller which is wrong.  This returns true on
success and false on failure.  But the caller assumes true is failure.
It suggests that this has not been tested.

> +
> +	return true;
> +}

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;

	mhi_cntrl->wakeup_host(mhi_cntrl);

	while (count++ < M0_WAIT_COUNT) {
		msleep(M0_WAIT_DELAY_MS);

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

> +
>  static int mhi_ep_send_event(struct mhi_ep_cntrl *mhi_cntrl, u32 ring_idx,
>  			     struct mhi_ring_element *el, bool bei)
>  {
> @@ -464,6 +485,13 @@ int mhi_ep_queue_skb(struct mhi_ep_device *mhi_dev, struct sk_buff *skb)
>  	buf_left = skb->len;
>  	ring = &mhi_cntrl->mhi_chan[mhi_chan->chan].ring;
>  
> +	if (mhi_cntrl->mhi_state == MHI_STATE_M3) {
> +		if (mhi_ep_wake_host(mhi_cntrl)) {
> +			dev_err(dev, "Failed to wakeup host\n");
> +			return -ENODEV;
> +		}

Then this becomes:

	if (mhi_cntrl->mhi_state == MHI_STATE_M3) {
		ret = mhi_ep_wake_host(mhi_cntrl);
		if (ret) {
			dev_err(dev, "Failed to wakeup host\n");
			return ret;
		}
	}

regards,
dan carpenter