linux-kernel - Re: [PATCH v8 1/3] Bluetooth: hci_qca: use wait_until

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Message-ID: <20190117161331.GW3691@localhost>
Date:   Thu, 17 Jan 2019 17:13:31 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Balakrishna Godavarthi <bgodavar@...eaurora.org>
Cc:     Matthias Kaehlcke <mka@...omium.org>, marcel@...tmann.org,
        johan.hedberg@...il.com, linux-kernel@...r.kernel.org,
        linux-bluetooth@...r.kernel.org, hemantg@...eaurora.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v8 1/3] Bluetooth: hci_qca: use wait_until_sent() for
 power pulses

On Thu, Jan 17, 2019 at 03:55:17PM +0530, Balakrishna Godavarthi wrote:
> Hi Matthias,
> 
> On 2019-01-17 01:52, Matthias Kaehlcke wrote:

> >> -	/* Wait for 100 uS for SoC to settle down */
> >> -	usleep_range(100, 200);
> >> +	serdev_device_wait_until_sent(hu->serdev, timeout);
> >> +	/* Wait of 5ms is required for assuring to send the byte on the Tx
> >> +	 * line and also for the controller to settle down for the received
> >> +	 * byte.
> >> +	 */
> >> +	usleep_range(5000, 6000);
> > 
> > I incorrectly claimed that there might be still bytes sitting in the
> > UART FIFO when serdev_device_wait_until_sent() returns, Johan
> > corrected me on that (thanks!). So if it takes the SoC 100us to settle
> > down we should be good with the original code.
> 
> [Bala]: sure will revert, i think he commented that wait_until_sent()
> will only guarantee circular buffer is empty. if wait_until_sent()
> guarantee us that the data was transmitted from the FIFO, then 100us
> will work.

No, Matthias is correct; I claimed that the UART FIFO will be empty (at
least as long as flow control is disabled, otherwise it may never empty
and we therefore also have a time out).

Johan