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

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Message-ID: <21ac40f7314788e2d25b97628f998eb3@codeaurora.org>
Date:   Thu, 17 Jan 2019 22:25:33 +0530
From:   Balakrishna Godavarthi <bgodavar@...eaurora.org>
To:     Johan Hovold <johan@...nel.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 2019-01-17 21:43, Johan Hovold wrote:
> 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

[Bala]: Thanks Johan for clarification.
-- 
Regards
Balakrishna.