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

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Date:   Tue, 11 Jul 2023 11:45:27 +0530
From:   Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Dan Carpenter <dan.carpenter@...aro.org>
CC:     <manivannan.sadhasivam@...aro.org>, <linux-pci@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <quic_vbadigan@...cinc.com>, <quic_nitegupt@...cinc.com>,
        <quic_skananth@...cinc.com>, <quic_ramkri@...cinc.com>,
        <krzysztof.kozlowski@...aro.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Jeffrey Hugo <quic_jhugo@...cinc.com>,
        Bo Liu <liubo03@...pur.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Dan Carpenter <error27@...il.com>,
        "open list:MHI BUS" <mhi@...ts.linux.dev>
Subject: Re: [PATCH v3 9/9] bus: mhi: ep: wake up host is the MHI state is in
 M3


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@...cinc.com>
>>> ---
>>>   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
> read.

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;
>>
>> 	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;
>> }