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 23:58:39 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Jonas Dreßler <verdre@...d.nl>
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 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.
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?


-- 
With Best Regards,
Andy Shevchenko