linux-kernel - Re: [PATCH 2/3] Bluetooth: hci_qca: Skip serdev wait when no transfer is pending

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Date:   Sat, 06 Jun 2020 18:27:59 +0530
From:   bgodavar@...eaurora.org
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        linux-bluetooth@...r.kernel.org,
        Rocky Liao <rjliao@...eaurora.org>,
        Zijun Hu <zijuhu@...eaurora.org>, linux-kernel@...r.kernel.org,
        Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
        Claire Chang <tientzu@...omium.org>, hemantg@...eaurora.org
Subject: Re: [PATCH 2/3] Bluetooth: hci_qca: Skip serdev wait when no transfer
 is pending

Hi matthias,

On 2020-06-06 00:16, Matthias Kaehlcke wrote:
> qca_suspend() calls serdev_device_wait_until_sent() regardless of
> whether a transfer is pending. While it does no active harm since
> the function should return immediately it makes the code more
> confusing. Add a flag to track whether a transfer is pending and
> only call serdev_device_wait_until_sent() is needed.
> 
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> ---
> 
>  drivers/bluetooth/hci_qca.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> index b1d82d32892e9..90ffd8ca1fb0d 100644
> --- a/drivers/bluetooth/hci_qca.c
> +++ b/drivers/bluetooth/hci_qca.c
> @@ -2050,6 +2050,7 @@ static int __maybe_unused qca_suspend(struct 
> device *dev)
>  	struct hci_uart *hu = &qcadev->serdev_hu;
>  	struct qca_data *qca = hu->priv;
>  	unsigned long flags;
> +	bool tx_pending = false;
>  	int ret = 0;
>  	u8 cmd;
> 
> @@ -2083,6 +2084,7 @@ static int __maybe_unused qca_suspend(struct 
> device *dev)
> 
>  		qca->tx_ibs_state = HCI_IBS_TX_ASLEEP;
>  		qca->ibs_sent_slps++;
> +		tx_pending = true;
>  		break;
> 
>  	case HCI_IBS_TX_ASLEEP:
> @@ -2099,8 +2101,10 @@ static int __maybe_unused qca_suspend(struct 
> device *dev)
>  	if (ret < 0)
>  		goto error;
> 
> -	serdev_device_wait_until_sent(hu->serdev,
> -				      msecs_to_jiffies(CMD_TRANS_TIMEOUT_MS));
> +	if (tx_pending) {
[Bala]: Good idea why don't we move this call to switch case under 
HCI_IBS_TX_AWAKE
https://elixir.bootlin.com/linux/latest/source/drivers/bluetooth/hci_qca.c#L1994

i.e. i would recommend below sequence

1. Send SLEEP BYTE
2. wait for some time to write SLEEP Byte on Tx line
3. call for Tx clock off qca_wq_serial_tx_clock_vote_off

> +		serdev_device_wait_until_sent(hu->serdev,
> +					      msecs_to_jiffies(CMD_TRANS_TIMEOUT_MS));
> +	}
> 
>  	/* Wait for HCI_IBS_SLEEP_IND sent by device to indicate its Tx is 
> going
>  	 * to sleep, so that the packet does not wake the system later.