Re: [PATCH v3 1/4] Bluetooth: hci_qca: use wait_until_sent() for power pulses

[Balakrishna Godavarthi]

Hi Johan,

On 2018-12-06 16:10, Balakrishna Godavarthi wrote:
> Hi Johan,
>
> On 2018-12-05 11:55, Johan Hovold wrote:
> > On Fri, Nov 30, 2018 at 08:32:44PM +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 <bgodavar@xxxxxxxxxxxxxx>
> > > ---
> > > v3:
> > >   * no change.
> > > v2:
> > >   * Updated function qca_send_power_pulse()
> > >   * addressed reviewer comments.
> >
> > Please make sure to include reviewers on CC when resending, and as
> > someone else already mentioned, be a bit more specific about what
> > changes you actually made in response to the review feedback you
> > received.
>
> [Bala]: sure will add and provide more info in version change history.
>
> > > v1:
> > >  * initial patch
> > > ---
> > >  drivers/bluetooth/hci_qca.c | 37 
> > > +++++++++++++------------------------
> > >  1 file changed, 13 insertions(+), 24 deletions(-)
> > >
> > > diff --git a/drivers/bluetooth/hci_qca.c 
> > > b/drivers/bluetooth/hci_qca.c
> > > index f036c8f98ea3..f5dd323c1967 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(hu->serdev, &cmd, sizeof(cmd), 0);
> >
> > You're still using 0 as a timeout here which is broken, as I already
> > told you.
>
> [Bala]: got the change now will update to timeout to non zero value.
>
> > From 4.21 this will result in an indefinite timeout, but currently
> > implies not to wait for a full write buffer to drain at all.
> >
> > As I also mentioned, you need to to make sure to call
> > serdev_device_write_wakeup() in the write_wakup() path if you are 
> > going
> > to use serdev_device_write() at all.
>
> [Bala]: this where i am confused.
>         calling serdev_device_write is calling an wakeup internally.
> below is the flow
>
>         ttyport_write_buf:
>               * calling serdev_device_write() will call write_buf() in
> this call we are enabling bit "TTY_DO_WRITE_WAKEUP" and calling
> write()
>                 i.e. uart_write() where we call in start_tx. this will
> go to the vendor specific write where in isr we call
> uart_write_wakeup()
>
> https://elixir.bootlin.com/linux/latest/source/drivers/tty/serial/qcom_geni_serial.c#L756
>
>
> uart_write_wakeup()->ttyport_write_wakeup()->serdev_controller_write_wakeup()->hci_uart_write_wakeup()->hci_uart_tx_wakeup()
>
>         the above is flow when serdev_device_write() is called, it is
> indirectly calling serdev_write_wakeup().
>
>         Why actual we need to call an serdev_write_wakeup() is this
> wakeup related to the UART port or for the BT chip.
>
> > Johan

Can you help me to understand, whether my understating is correct wrt 
serdev_wakeup().

--
Regards
Balakrishna.