From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthias Kaehlcke Subject: Re: [PATCH v5 1/5] Bluetooth: hci_qca: use wait_until_sent() for power pulses Date: Fri, 11 Jan 2019 15:38:12 -0800 Message-ID: <20190111233812.GJ261387@google.com> References: <20181220144639.15928-1-bgodavar@codeaurora.org> <20181220144639.15928-2-bgodavar@codeaurora.org> <20181222015947.GF261387@google.com> <20190109143822.GM14782@localhost> <2d4ee183e3c2fa964c14a5ac702043c0@codeaurora.org> <20190111005532.GC261387@google.com> <5e4b077bbcc81b624c851643bebc45f7@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <5e4b077bbcc81b624c851643bebc45f7@codeaurora.org> Sender: linux-kernel-owner@vger.kernel.org To: Balakrishna Godavarthi Cc: Johan Hovold , marcel@holtmann.org, johan.hedberg@gmail.com, linux-kernel@vger.kernel.org, linux-bluetooth@vger.kernel.org, hemantg@codeaurora.org, linux-arm-msm@vger.kernel.org, Johan Hovold List-Id: linux-arm-msm@vger.kernel.org On Fri, Jan 11, 2019 at 08:02:00PM +0530, Balakrishna Godavarthi wrote: > On 2019-01-11 06:25, Matthias Kaehlcke wrote: > > On Thu, Jan 10, 2019 at 08:18:37PM +0530, Balakrishna Godavarthi wrote: > > > Hi Johan, > > > > > > On 2019-01-09 20:08, Johan Hovold wrote: > > > > On Fri, Dec 21, 2018 at 05:59:47PM -0800, Matthias Kaehlcke wrote: > > > > > On Thu, Dec 20, 2018 at 08:16:35PM +0530, Balakrishna Godavarthi > > > > > wrote: > > > > > > wcn3990 requires a power pulse to turn ON/OFF along with > > > > > > regulators. Sometimes we are observing the power pulses are sent > > > > > > out with some time delay, due to queuing these commands. This is > > > > > > causing synchronization issues with chip, which intern delay the > > > > > > chip setup or may end up with communication issues. > > > > > > > > > > > > Signed-off-by: Balakrishna Godavarthi > > > > > > --- > > > > > > drivers/bluetooth/hci_qca.c | 38 ++++++++++++++----------------------- > > > > > > 1 file changed, 14 insertions(+), 24 deletions(-) > > > > > > > > > > > > diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c > > > > > > index f036c8f98ea3..5a07c2370289 100644 > > > > > > --- a/drivers/bluetooth/hci_qca.c > > > > > > +++ b/drivers/bluetooth/hci_qca.c > > > > > > @@ -1013,11 +1013,9 @@ static inline void host_set_baudrate(struct hci_uart *hu, unsigned int speed) > > > > > > hci_uart_set_baudrate(hu, speed); > > > > > > } > > > > > > > > > > > > -static int qca_send_power_pulse(struct hci_dev *hdev, u8 cmd) > > > > > > +static int qca_send_power_pulse(struct hci_uart *hu, u8 cmd) > > > > > > { > > > > > > - struct hci_uart *hu = hci_get_drvdata(hdev); > > > > > > - struct qca_data *qca = hu->priv; > > > > > > - struct sk_buff *skb; > > > > > > + int ret; > > > > > > > > > > > > /* These power pulses are single byte command which are sent > > > > > > * at required baudrate to wcn3990. On wcn3990, we have an external > > > > > > @@ -1029,19 +1027,16 @@ static int qca_send_power_pulse(struct hci_dev *hdev, u8 cmd) > > > > > > * save power. Disabling hardware flow control is mandatory while > > > > > > * sending power pulses to SoC. > > > > > > */ > > > > > > - bt_dev_dbg(hdev, "sending power pulse %02x to SoC", cmd); > > > > > > - > > > > > > - skb = bt_skb_alloc(sizeof(cmd), GFP_KERNEL); > > > > > > - if (!skb) > > > > > > - return -ENOMEM; > > > > > > - > > > > > > + bt_dev_dbg(hu->hdev, "sending power pulse %02x to SoC", cmd); > > > > > > hci_uart_set_flow_control(hu, true); > > > > > > + ret = serdev_device_write_buf(hu->serdev, &cmd, sizeof(cmd)); > > > > > > + if (ret < 0) { > > > > > > + bt_dev_err(hu->hdev, "failed to send power pulse %02x to SoC", > > > > > > + cmd); > > > > > > + return ret; > > > > > > + } > > > > > > > > > > > > - skb_put_u8(skb, cmd); > > > > > > - hci_skb_pkt_type(skb) = HCI_COMMAND_PKT; > > > > > > - > > > > > > - skb_queue_tail(&qca->txq, skb); > > > > > > - hci_uart_tx_wakeup(hu); > > > > > > + serdev_device_wait_until_sent(hu->serdev, 0); > > > > > > > > Again, do you really want to wait indefinitely here? > > > > > > > [Bala]: these commands are mandatory to turn ON or OFF the chip. > > > so blocking to the max time is required. > > > these commands are sent during the BT chip ON & OFF. > > > in the latest series, i have flushed the uart before sending > > > this > > > commands > > > so the uart FIFO(as just opened the port before calling this > > > function) or the circular > > > buffer will be empty and also i am disabling the flow > > > control too. > > > https://patchwork.kernel.org/patch/10744435/ > > > > The commands may be mandatory for switching the chip on or off, but > > what is better if there is a problem with sending them (e.g. a buggy > > UART driver): > > > > 1. wait a reasonable time, report an error > > 2. wait forever > > > > ? > > > > If the single byte command couldn't be sent after a few milliseconds, > > it likely never will, waiting forever doesn't fix that. An error > > report at least provides some information about the problem and the > > driver is in a not-hanging state. > > > > Cheers > > > > Matthias > > [Bala]: will update this with a bound TIMEOUT value. But wait_until_sent() > is void return > type how could we know that the data is sent out on the lines. Good point, I didn't check and expected it to return an error. If you feel really motivated and have maintainer support you could possibly change the API, however it seems this would be a somewhat larger change. I guess the next best thing to do is to proceed as if all data was sent and if there was a problem it will likely manifest through another error (especially for the ON pulse), which still seems better than a hanging driver. Cheers Matthias