linux-kernel - Re: [PATCH v2 2/2] mwifiex: Try waking the firmware until we get an interrupt

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Date:   Thu, 30 Sep 2021 23:07:09 +0200
From:   Jonas Dreßler <verdre@...d.nl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Amitkumar Karwar <amitkarwar@...il.com>,
        Ganapathi Bhat <ganapathi017@...il.com>,
        Xinming Hu <huxinming820@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Tsuchiya Yuto <kitakar@...il.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        Maximilian Luz <luzmaximilian@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Pali Rohár <pali@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Johannes Berg <johannes@...solutions.net>,
        Brian Norris <briannorris@...omium.org>, stable@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mwifiex: Try waking the firmware until we get an
 interrupt

On 9/30/21 10:58 PM, Andy Shevchenko wrote:
> On Thu, Sep 30, 2021 at 08:04:00PM +0200, Jonas Dreßler wrote:
>> On 9/22/21 1:19 PM, Andy Shevchenko wrote:
>>> On Tue, Sep 14, 2021 at 01:48:13PM +0200, Jonas Dreßler wrote:
> 
> ...
> 
>>>> +	do {
>>>> +		if (mwifiex_write_reg(adapter, reg->fw_status, FIRMWARE_READY_PCIE)) {
>>>> +			mwifiex_dbg(adapter, ERROR,
>>>> +				    "Writing fw_status register failed\n");
>>>> +			return -EIO;
>>>> +		}
>>>> +
>>>> +		n_tries++;
>>>> +
>>>> +		if (n_tries <= N_WAKEUP_TRIES_SHORT_INTERVAL)
>>>> +			usleep_range(400, 700);
>>>> +		else
>>>> +			msleep(10);
>>>> +	} while (n_tries <= N_WAKEUP_TRIES_SHORT_INTERVAL + N_WAKEUP_TRIES_LONG_INTERVAL &&
>>>> +		 READ_ONCE(adapter->int_status) == 0);
>>>
>>> Can't you use read_poll_timeout() twice instead of this custom approach?
>>
>> I've tried this now, but read_poll_timeout() is not ideal for our use-case.
>> What we'd need would be read->sleep->poll->repeat instead of
>> read->poll->sleep->repeat. With read_poll_timeout() we always end up doing
>> one more (unnecessary) write.
> 
> First of all, there is a parameter to get sleep beforehand.

Sleeping beforehand will sleep before doing the first write, so that's 
just wasted time.

> Second, what is the problem with having one write more or less?
> Your current code doesn't guarantee this either. It only decreases
> probability of such scenario. Am I wrong?
> 
> 

Indeed my approach just decreases the probability and we sometimes end 
up writing twice to wakeup the card, but it would kinda bug me if we'd 
always do one write too much.

Anyway, if you still prefer the read_poll_timeout() solution I'd be 
alright with that of course.