Changes in V2:
- As per Matthias's comment added wakeup support for all the UARTs
of SC7180.
- Added sleep state in sc7180-idp.dts file.
- Modify the if check in set_mctrl API in serial driver to avoid
making RFR high during suspend.
Hi Greg,
These patches are based on qcom tree. Please ack the serial driver
patch to land via qcom-tree.
Thanks,
Satya Priya
satya priya (3):
arm64: dts: sc7180: Add wakeup support over UART RX
arm64: dts: qcom: sc7180: Add sleep pin ctrl for BT uart
tty: serial: qcom_geni_serial: Fix the UART wakeup issue
arch/arm64/boot/dts/qcom/sc7180-idp.dts | 42 ++++++++++++--
arch/arm64/boot/dts/qcom/sc7180.dtsi | 98 ++++++++++++++++++++++++++++-----
drivers/tty/serial/qcom_geni_serial.c | 2 +-
3 files changed, 121 insertions(+), 21 deletions(-)
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation
Add sleep pin ctrl for BT uart, and also change the bias
configuration to match Bluetooth module.
Signed-off-by: satya priya <[email protected]>
---
Changes in V2:
- This patch adds sleep state for BT UART. Newly added in V2.
arch/arm64/boot/dts/qcom/sc7180-idp.dts | 42 ++++++++++++++++++++++++++++-----
1 file changed, 36 insertions(+), 6 deletions(-)
diff --git a/arch/arm64/boot/dts/qcom/sc7180-idp.dts b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
index 26cc491..bc919f2 100644
--- a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
+++ b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
@@ -469,20 +469,50 @@
&qup_uart3_default {
pinconf-cts {
- /*
- * Configure a pull-down on 38 (CTS) to match the pull of
- * the Bluetooth module.
- */
+ /* Configure no pull on 38 (CTS) to match Bluetooth module */
pins = "gpio38";
+ bias-disable;
+ };
+
+ pinconf-rts {
+ /* We'll drive 39 (RTS), so configure pull-down */
+ pins = "gpio39";
+ drive-strength = <2>;
bias-pull-down;
+ };
+
+ pinconf-tx {
+ /* We'll drive 40 (TX), so no pull */
+ pins = "gpio40";
+ drive-strength = <2>;
+ bias-disable;
output-high;
};
+ pinconf-rx {
+ /*
+ * Configure a pull-up on 41 (RX). This is needed to avoid
+ * garbage data when the TX pin of the Bluetooth module is
+ * in tri-state (module powered off or not driving the
+ * signal yet).
+ */
+ pins = "gpio41";
+ bias-pull-up;
+ };
+};
+
+&qup_uart3_sleep {
+ pinconf-cts {
+ /* Configure no-pull on 38 (CTS) to match Bluetooth module */
+ pins = "gpio38";
+ bias-disable;
+ };
+
pinconf-rts {
- /* We'll drive 39 (RTS), so no pull */
+ /* We'll drive 39 (RTS), so configure pull-down */
pins = "gpio39";
drive-strength = <2>;
- bias-disable;
+ bias-pull-down;
};
pinconf-tx {
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation
As a part of system suspend we call uart_port_suspend from the
Serial driver, which calls set_mctrl passing mctrl as NULL. This
makes RFR high(NOT_READY) during suspend.
Due to this BT SoC is not able to send wakeup bytes to UART during
suspend. Included if check for non-suspend case to keep RFR low
during suspend.
Signed-off-by: satya priya <[email protected]>
---
Changes in V2:
- This patch fixes the UART flow control issue during suspend.
Newly added in V2.
drivers/tty/serial/qcom_geni_serial.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index 07b7b6b..7108dfc 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -242,7 +242,7 @@ static void qcom_geni_serial_set_mctrl(struct uart_port *uport,
if (mctrl & TIOCM_LOOP)
port->loopback = RX_TX_CTS_RTS_SORTED;
- if (!(mctrl & TIOCM_RTS))
+ if ((!(mctrl & TIOCM_RTS)) && (!(uport->suspended)))
uart_manual_rfr = UART_MANUAL_RFR_EN | UART_RFR_NOT_READY;
writel(uart_manual_rfr, uport->membase + SE_UART_MANUAL_RFR);
}
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation
On Fri, Jul 24, 2020 at 09:28:02AM +0530, satya priya wrote:
> As a part of system suspend we call uart_port_suspend from the
> Serial driver, which calls set_mctrl passing mctrl as NULL. This
> makes RFR high(NOT_READY) during suspend.
>
> Due to this BT SoC is not able to send wakeup bytes to UART during
> suspend. Included if check for non-suspend case to keep RFR low
> during suspend.
>
> Signed-off-by: satya priya <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
On 7/24/2020 9:28 AM, satya priya wrote:
> Add sleep pin ctrl for BT uart, and also change the bias
> configuration to match Bluetooth module.
Reviewed-by: Akash Asthana <[email protected]>
> Signed-off-by: satya priya <[email protected]>
> ---
> Changes in V2:
> - This patch adds sleep state for BT UART. Newly added in V2.
>
> arch/arm64/boot/dts/qcom/sc7180-idp.dts | 42 ++++++++++++++++++++++++++++-----
> 1 file changed, 36 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/boot/dts/qcom/sc7180-idp.dts b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> index 26cc491..bc919f2 100644
> --- a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> +++ b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> @@ -469,20 +469,50 @@
>
> &qup_uart3_default {
> pinconf-cts {
> - /*
> - * Configure a pull-down on 38 (CTS) to match the pull of
> - * the Bluetooth module.
> - */
> + /* Configure no pull on 38 (CTS) to match Bluetooth module */
> pins = "gpio38";
> + bias-disable;
> + };
> +
> + pinconf-rts {
> + /* We'll drive 39 (RTS), so configure pull-down */
> + pins = "gpio39";
> + drive-strength = <2>;
> bias-pull-down;
> + };
> +
> + pinconf-tx {
> + /* We'll drive 40 (TX), so no pull */
> + pins = "gpio40";
> + drive-strength = <2>;
> + bias-disable;
> output-high;
> };
>
> + pinconf-rx {
> + /*
> + * Configure a pull-up on 41 (RX). This is needed to avoid
> + * garbage data when the TX pin of the Bluetooth module is
> + * in tri-state (module powered off or not driving the
> + * signal yet).
> + */
> + pins = "gpio41";
> + bias-pull-up;
> + };
> +};
> +
> +&qup_uart3_sleep {
> + pinconf-cts {
> + /* Configure no-pull on 38 (CTS) to match Bluetooth module */
> + pins = "gpio38";
> + bias-disable;
> + };
> +
> pinconf-rts {
> - /* We'll drive 39 (RTS), so no pull */
> + /* We'll drive 39 (RTS), so configure pull-down */
> pins = "gpio39";
> drive-strength = <2>;
> - bias-disable;
> + bias-pull-down;
> };
>
> pinconf-tx {
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,\na Linux Foundation Collaborative Project
On 7/24/2020 9:28 AM, satya priya wrote:
> As a part of system suspend we call uart_port_suspend from the
> Serial driver, which calls set_mctrl passing mctrl as NULL. This
> makes RFR high(NOT_READY) during suspend.
>
> Due to this BT SoC is not able to send wakeup bytes to UART during
> suspend. Included if check for non-suspend case to keep RFR low
> during suspend.
Reviewed-by: Akash Asthana <[email protected]>
> Signed-off-by: satya priya <[email protected]>
> ---
> Changes in V2:
> - This patch fixes the UART flow control issue during suspend.
> Newly added in V2.
>
> drivers/tty/serial/qcom_geni_serial.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index 07b7b6b..7108dfc 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -242,7 +242,7 @@ static void qcom_geni_serial_set_mctrl(struct uart_port *uport,
> if (mctrl & TIOCM_LOOP)
> port->loopback = RX_TX_CTS_RTS_SORTED;
>
> - if (!(mctrl & TIOCM_RTS))
> + if ((!(mctrl & TIOCM_RTS)) && (!(uport->suspended)))
> uart_manual_rfr = UART_MANUAL_RFR_EN | UART_RFR_NOT_READY;
> writel(uart_manual_rfr, uport->membase + SE_UART_MANUAL_RFR);
> }
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,\na Linux Foundation Collaborative Project
On Fri, Jul 24, 2020 at 09:28:02AM +0530, satya priya wrote:
> As a part of system suspend we call uart_port_suspend from the
> Serial driver, which calls set_mctrl passing mctrl as NULL. This
> makes RFR high(NOT_READY) during suspend.
>
> Due to this BT SoC is not able to send wakeup bytes to UART during
> suspend. Included if check for non-suspend case to keep RFR low
> during suspend.
>
> Signed-off-by: satya priya <[email protected]>
> ---
> Changes in V2:
> - This patch fixes the UART flow control issue during suspend.
> Newly added in V2.
>
> drivers/tty/serial/qcom_geni_serial.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index 07b7b6b..7108dfc 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -242,7 +242,7 @@ static void qcom_geni_serial_set_mctrl(struct uart_port *uport,
> if (mctrl & TIOCM_LOOP)
> port->loopback = RX_TX_CTS_RTS_SORTED;
>
> - if (!(mctrl & TIOCM_RTS))
> + if ((!(mctrl & TIOCM_RTS)) && (!(uport->suspended)))
Why all these parentheses, instead of:
if (!(mctrl & TIOCM_RTS) && !uport->suspended)
?
On Fri, Jul 24, 2020 at 09:28:01AM +0530, satya priya wrote:
> Add sleep pin ctrl for BT uart, and also change the bias
> configuration to match Bluetooth module.
>
> Signed-off-by: satya priya <[email protected]>
> ---
> Changes in V2:
> - This patch adds sleep state for BT UART. Newly added in V2.
>
> arch/arm64/boot/dts/qcom/sc7180-idp.dts | 42 ++++++++++++++++++++++++++++-----
> 1 file changed, 36 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/boot/dts/qcom/sc7180-idp.dts b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> index 26cc491..bc919f2 100644
> --- a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> +++ b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> @@ -469,20 +469,50 @@
>
> &qup_uart3_default {
> pinconf-cts {
> - /*
> - * Configure a pull-down on 38 (CTS) to match the pull of
> - * the Bluetooth module.
> - */
> + /* Configure no pull on 38 (CTS) to match Bluetooth module */
Has the pull from the Bluetooth module been removed or did the previous config
incorrectly claim that the Bluetooth module has a pull-down?
> pins = "gpio38";
> + bias-disable;
> + };
> +
> + pinconf-rts {
> + /* We'll drive 39 (RTS), so configure pull-down */
> + pins = "gpio39";
> + drive-strength = <2>;
> bias-pull-down;
> + };
> +
> + pinconf-tx {
> + /* We'll drive 40 (TX), so no pull */
The rationales for RTS and TX contradict each other. According to the comment
the reason to configure a pull-down on RTS is that it is driven by the host.
Then for TX the reason to configure no pull is that it is driven by the host.
Please make sure the comments *really* describe the rationale, otherwise they
are just confusing.
On Mon, Aug 17, 2020 at 11:01:58AM -0700, Matthias Kaehlcke wrote:
> On Fri, Jul 24, 2020 at 09:28:01AM +0530, satya priya wrote:
> > Add sleep pin ctrl for BT uart, and also change the bias
> > configuration to match Bluetooth module.
> >
> > Signed-off-by: satya priya <[email protected]>
> > ---
> > Changes in V2:
> > - This patch adds sleep state for BT UART. Newly added in V2.
> >
> > arch/arm64/boot/dts/qcom/sc7180-idp.dts | 42 ++++++++++++++++++++++++++++-----
> > 1 file changed, 36 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/arm64/boot/dts/qcom/sc7180-idp.dts b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> > index 26cc491..bc919f2 100644
> > --- a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> > +++ b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> > @@ -469,20 +469,50 @@
> >
> > &qup_uart3_default {
> > pinconf-cts {
> > - /*
> > - * Configure a pull-down on 38 (CTS) to match the pull of
> > - * the Bluetooth module.
> > - */
> > + /* Configure no pull on 38 (CTS) to match Bluetooth module */
>
> Has the pull from the Bluetooth module been removed or did the previous config
> incorrectly claim that the Bluetooth module has a pull-down?
>
> > pins = "gpio38";
> > + bias-disable;
> > + };
> > +
> > + pinconf-rts {
> > + /* We'll drive 39 (RTS), so configure pull-down */
> > + pins = "gpio39";
> > + drive-strength = <2>;
> > bias-pull-down;
> > + };
> > +
> > + pinconf-tx {
> > + /* We'll drive 40 (TX), so no pull */
>
> The rationales for RTS and TX contradict each other. According to the comment
> the reason to configure a pull-down on RTS is that it is driven by the host.
> Then for TX the reason to configure no pull is that it is driven by the host.
>
> Please make sure the comments *really* describe the rationale, otherwise they
> are just confusing.
Ok, let's try to reason about the configurations.
I didn't find the datasheet for the WCN3991, but my understanding is that
it is an evolution of the WCN3998, so probably the states of the UART pins
are the same (signal names from the BT chip perspective):
active reset
CTS NP PD
RTS NP PD
RX NP PU
TX NP PD
Since this patch changes the DT let's use the signal names from the host side
in the following.
> RTS: NP => PD
I can see that this could make sense, a floating pin could indicate
the Bluetooth controller that the host is ready to receive data, when it is
not.
> CTS: PD => NP
From a signalling perspective this should be no problem, since the WCN399x
has a pull-down on its RTS signal in reset, and otherwise will drive it.
IIUC there should be no power leakage without a pull, so I think this
should be ok.
> TX: +output-high
IIUC this only has an impact when the pin is in GPIO mode, i.e. in the sleep
config. If that's correct, does it even make sense to specify it in the default
config?
Besides that, what is the reason for this change? I was told in another forum
that Qualcomm found this to fix problems at UART initialization and wakeup,
without really understanding why. That's not great.
I'm no expert in this area, but my guess is that forcing the TX signal to high
in certain states is needed to not have it floating (no pull is configured),
which could generate garbage on the Bluetooth RX side. But is it really
necessary to actively drive it to high? Wouldn't it be enough to configure a
pull-up when it isn't actively driven (i.e. in sleep mode)?
In a quick test wakeup from Bluetooth worked when configuring a pull-up only in
sleep mode. Could you test this on your side or provide a rationale why TX needs
to be actively driven to high?
Thanks
Matthias
On 2020-08-17 23:12, Matthias Kaehlcke wrote:
> On Fri, Jul 24, 2020 at 09:28:02AM +0530, satya priya wrote:
>> As a part of system suspend we call uart_port_suspend from the
>> Serial driver, which calls set_mctrl passing mctrl as NULL. This
>> makes RFR high(NOT_READY) during suspend.
>>
>> Due to this BT SoC is not able to send wakeup bytes to UART during
>> suspend. Included if check for non-suspend case to keep RFR low
>> during suspend.
>>
>> Signed-off-by: satya priya <[email protected]>
>> ---
>> Changes in V2:
>> - This patch fixes the UART flow control issue during suspend.
>> Newly added in V2.
>>
>> drivers/tty/serial/qcom_geni_serial.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/tty/serial/qcom_geni_serial.c
>> b/drivers/tty/serial/qcom_geni_serial.c
>> index 07b7b6b..7108dfc 100644
>> --- a/drivers/tty/serial/qcom_geni_serial.c
>> +++ b/drivers/tty/serial/qcom_geni_serial.c
>> @@ -242,7 +242,7 @@ static void qcom_geni_serial_set_mctrl(struct
>> uart_port *uport,
>> if (mctrl & TIOCM_LOOP)
>> port->loopback = RX_TX_CTS_RTS_SORTED;
>>
>> - if (!(mctrl & TIOCM_RTS))
>> + if ((!(mctrl & TIOCM_RTS)) && (!(uport->suspended)))
>
> Why all these parentheses, instead of:
>
> if (!(mctrl & TIOCM_RTS) && !uport->suspended)
>
> ?
ok. Will remove the extra parentheses.
On 2020-08-17 23:31, Matthias Kaehlcke wrote:
> On Fri, Jul 24, 2020 at 09:28:01AM +0530, satya priya wrote:
>> Add sleep pin ctrl for BT uart, and also change the bias
>> configuration to match Bluetooth module.
>>
>> Signed-off-by: satya priya <[email protected]>
>> ---
>> Changes in V2:
>> - This patch adds sleep state for BT UART. Newly added in V2.
>>
>> arch/arm64/boot/dts/qcom/sc7180-idp.dts | 42
>> ++++++++++++++++++++++++++++-----
>> 1 file changed, 36 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
>> b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
>> index 26cc491..bc919f2 100644
>> --- a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
>> +++ b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
>> @@ -469,20 +469,50 @@
>>
>> &qup_uart3_default {
>> pinconf-cts {
>> - /*
>> - * Configure a pull-down on 38 (CTS) to match the pull of
>> - * the Bluetooth module.
>> - */
>> + /* Configure no pull on 38 (CTS) to match Bluetooth module */
>
> Has the pull from the Bluetooth module been removed or did the previous
> config
> incorrectly claim that the Bluetooth module has a pull-down?
>
The previous config was incorrect, so we corrected it to match the pull
of BT.
>> pins = "gpio38";
>> + bias-disable;
>> + };
>> +
>> + pinconf-rts {
>> + /* We'll drive 39 (RTS), so configure pull-down */
>> + pins = "gpio39";
>> + drive-strength = <2>;
>> bias-pull-down;
>> + };
>> +
>> + pinconf-tx {
>> + /* We'll drive 40 (TX), so no pull */
>
> The rationales for RTS and TX contradict each other. According to the
> comment
> the reason to configure a pull-down on RTS is that it is driven by the
> host.
> Then for TX the reason to configure no pull is that it is driven by the
> host.
>
> Please make sure the comments *really* describe the rationale,
> otherwise they
> are just confusing.
The rationale for RTS is that we don't want it to be floating and want
to make sure that it is pulled down, to receive bytes. Will modify the
comment mentioning the same.
Hi Matthias,
Thanks for reviewing the patches.
On 2020-08-18 05:03, Matthias Kaehlcke wrote:
> On Mon, Aug 17, 2020 at 11:01:58AM -0700, Matthias Kaehlcke wrote:
>> On Fri, Jul 24, 2020 at 09:28:01AM +0530, satya priya wrote:
>> > Add sleep pin ctrl for BT uart, and also change the bias
>> > configuration to match Bluetooth module.
>> >
>> > Signed-off-by: satya priya <[email protected]>
>> > ---
>> > Changes in V2:
>> > - This patch adds sleep state for BT UART. Newly added in V2.
>> >
>> > arch/arm64/boot/dts/qcom/sc7180-idp.dts | 42 ++++++++++++++++++++++++++++-----
>> > 1 file changed, 36 insertions(+), 6 deletions(-)
>> >
>> > diff --git a/arch/arm64/boot/dts/qcom/sc7180-idp.dts b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
>> > index 26cc491..bc919f2 100644
>> > --- a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
>> > +++ b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
>> > @@ -469,20 +469,50 @@
>> >
>> > &qup_uart3_default {
>> > pinconf-cts {
>> > - /*
>> > - * Configure a pull-down on 38 (CTS) to match the pull of
>> > - * the Bluetooth module.
>> > - */
>> > + /* Configure no pull on 38 (CTS) to match Bluetooth module */
>>
>> Has the pull from the Bluetooth module been removed or did the
>> previous config
>> incorrectly claim that the Bluetooth module has a pull-down?
>>
>> > pins = "gpio38";
>> > + bias-disable;
>> > + };
>> > +
>> > + pinconf-rts {
>> > + /* We'll drive 39 (RTS), so configure pull-down */
>> > + pins = "gpio39";
>> > + drive-strength = <2>;
>> > bias-pull-down;
>> > + };
>> > +
>> > + pinconf-tx {
>> > + /* We'll drive 40 (TX), so no pull */
>>
>> The rationales for RTS and TX contradict each other. According to the
>> comment
>> the reason to configure a pull-down on RTS is that it is driven by the
>> host.
>> Then for TX the reason to configure no pull is that it is driven by
>> the host.
>>
>> Please make sure the comments *really* describe the rationale,
>> otherwise they
>> are just confusing.
>
> Ok, let's try to reason about the configurations.
>
> I didn't find the datasheet for the WCN3991, but my understanding is
> that
> it is an evolution of the WCN3998, so probably the states of the UART
> pins
> are the same (signal names from the BT chip perspective):
>
> active reset
> CTS NP PD
> RTS NP PD
> RX NP PU
> TX NP PD
>
> Since this patch changes the DT let's use the signal names from the
> host side
> in the following.
>
>> RTS: NP => PD
>
> I can see that this could make sense, a floating pin could indicate
> the Bluetooth controller that the host is ready to receive data, when
> it is
> not.
>
>> CTS: PD => NP
>
> From a signalling perspective this should be no problem, since the
> WCN399x
> has a pull-down on its RTS signal in reset, and otherwise will drive
> it.
> IIUC there should be no power leakage without a pull, so I think this
> should be ok.
>
With CTS having no-pull, we are not seeing any power leakages.
>> TX: +output-high
>
> IIUC this only has an impact when the pin is in GPIO mode, i.e. in the
> sleep
> config. If that's correct, does it even make sense to specify it in the
> default
> config?
>
> Besides that, what is the reason for this change? I was told in another
> forum
> that Qualcomm found this to fix problems at UART initialization and
> wakeup,
> without really understanding why. That's not great.
>
"output-high" was present in IDP dts since Bring-up, we've validated on
the latest code-base and see that "output-high" is not required, will
remove it.
> I'm no expert in this area, but my guess is that forcing the TX signal
> to high
> in certain states is needed to not have it floating (no pull is
> configured),
> which could generate garbage on the Bluetooth RX side. But is it really
> necessary to actively drive it to high? Wouldn't it be enough to
> configure a
> pull-up when it isn't actively driven (i.e. in sleep mode)?
>
> In a quick test wakeup from Bluetooth worked when configuring a pull-up
> only in
> sleep mode. Could you test this on your side or provide a rationale why
> TX needs
> to be actively driven to high?
>
We have tested by keeping pull-up for TX in sleep state(removed
output-high) and wakeup is working fine with Bluetooth. Will remove the
output-high from both default and sleep states.
> Thanks
>
> Matthias
Thanks,
Satya Priya
On Wed, Aug 19, 2020 at 07:19:25PM +0530, [email protected] wrote:
> On 2020-08-17 23:31, Matthias Kaehlcke wrote:
> > On Fri, Jul 24, 2020 at 09:28:01AM +0530, satya priya wrote:
> > > Add sleep pin ctrl for BT uart, and also change the bias
> > > configuration to match Bluetooth module.
> > >
> > > Signed-off-by: satya priya <[email protected]>
> > > ---
> > > Changes in V2:
> > > - This patch adds sleep state for BT UART. Newly added in V2.
> > >
> > > arch/arm64/boot/dts/qcom/sc7180-idp.dts | 42
> > > ++++++++++++++++++++++++++++-----
> > > 1 file changed, 36 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> > > b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> > > index 26cc491..bc919f2 100644
> > > --- a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> > > +++ b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> > > @@ -469,20 +469,50 @@
> > >
> > > &qup_uart3_default {
> > > pinconf-cts {
> > > - /*
> > > - * Configure a pull-down on 38 (CTS) to match the pull of
> > > - * the Bluetooth module.
> > > - */
> > > + /* Configure no pull on 38 (CTS) to match Bluetooth module */
> >
> > Has the pull from the Bluetooth module been removed or did the previous
> > config
> > incorrectly claim that the Bluetooth module has a pull-down?
> >
>
> The previous config was incorrect, so we corrected it to match the pull of
> BT.
The pull config of the BT controller varies depending on its state, could
you clarify which state you intend to match?
>
> > > pins = "gpio38";
> > > + bias-disable;
> > > + };
> > > +
> > > + pinconf-rts {
> > > + /* We'll drive 39 (RTS), so configure pull-down */
> > > + pins = "gpio39";
> > > + drive-strength = <2>;
> > > bias-pull-down;
> > > + };
> > > +
> > > + pinconf-tx {
> > > + /* We'll drive 40 (TX), so no pull */
> >
> > The rationales for RTS and TX contradict each other. According to the
> > comment
> > the reason to configure a pull-down on RTS is that it is driven by the
> > host.
> > Then for TX the reason to configure no pull is that it is driven by the
> > host.
> >
> > Please make sure the comments *really* describe the rationale, otherwise
> > they
> > are just confusing.
>
> The rationale for RTS is that we don't want it to be floating and want to
> make sure that it is pulled down, to receive bytes. Will modify the comment
> mentioning the same.
Could you clarify what you mean with "to receive bytes"?
Thanks
Matthias
Hi Matthias,
On 2020-08-19 21:43, Matthias Kaehlcke wrote:
> On Wed, Aug 19, 2020 at 07:19:25PM +0530, [email protected] wrote:
>> On 2020-08-17 23:31, Matthias Kaehlcke wrote:
>> > On Fri, Jul 24, 2020 at 09:28:01AM +0530, satya priya wrote:
>> > > Add sleep pin ctrl for BT uart, and also change the bias
>> > > configuration to match Bluetooth module.
>> > >
>> > > Signed-off-by: satya priya <[email protected]>
>> > > ---
>> > > Changes in V2:
>> > > - This patch adds sleep state for BT UART. Newly added in V2.
>> > >
>> > > arch/arm64/boot/dts/qcom/sc7180-idp.dts | 42
>> > > ++++++++++++++++++++++++++++-----
>> > > 1 file changed, 36 insertions(+), 6 deletions(-)
>> > >
>> > > diff --git a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
>> > > b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
>> > > index 26cc491..bc919f2 100644
>> > > --- a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
>> > > +++ b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
>> > > @@ -469,20 +469,50 @@
>> > >
>> > > &qup_uart3_default {
>> > > pinconf-cts {
>> > > - /*
>> > > - * Configure a pull-down on 38 (CTS) to match the pull of
>> > > - * the Bluetooth module.
>> > > - */
>> > > + /* Configure no pull on 38 (CTS) to match Bluetooth module */
>> >
>> > Has the pull from the Bluetooth module been removed or did the previous
>> > config
>> > incorrectly claim that the Bluetooth module has a pull-down?
>> >
>>
>> The previous config was incorrect, so we corrected it to match the
>> pull of
>> BT.
>
> The pull config of the BT controller varies depending on its state,
> could
> you clarify which state you intend to match?
>
Since this line is driven by BT SoC, they could change their
pull(although it's less likely). Recently on cherokee we worked with BT
team and came to an agreement to keep no-pull from our side in order to
not conflict with their pull in any state.
>>
>> > > pins = "gpio38";
>> > > + bias-disable;
>> > > + };
>> > > +
>> > > + pinconf-rts {
>> > > + /* We'll drive 39 (RTS), so configure pull-down */
>> > > + pins = "gpio39";
>> > > + drive-strength = <2>;
>> > > bias-pull-down;
>> > > + };
>> > > +
>> > > + pinconf-tx {
>> > > + /* We'll drive 40 (TX), so no pull */
>> >
>> > The rationales for RTS and TX contradict each other. According to the
>> > comment
>> > the reason to configure a pull-down on RTS is that it is driven by the
>> > host.
>> > Then for TX the reason to configure no pull is that it is driven by the
>> > host.
>> >
>> > Please make sure the comments *really* describe the rationale, otherwise
>> > they
>> > are just confusing.
>>
>> The rationale for RTS is that we don't want it to be floating and want
>> to
>> make sure that it is pulled down, to receive bytes. Will modify the
>> comment
>> mentioning the same.
>
> Could you clarify what you mean with "to receive bytes"?
>
When we keep no-pull(floating), sometimes it may be pulled high and UART
flow will be turned off(RFR_NOT_READY), due to this BT SoC wont be able
to send data even though host is ready.
> Thanks
>
> Matthias
Thanks,
Satya Priya
On Thu, Aug 20, 2020 at 05:49:53PM +0530, [email protected] wrote:
> Hi Matthias,
>
> On 2020-08-19 21:43, Matthias Kaehlcke wrote:
> > On Wed, Aug 19, 2020 at 07:19:25PM +0530, [email protected] wrote:
> > > On 2020-08-17 23:31, Matthias Kaehlcke wrote:
> > > > On Fri, Jul 24, 2020 at 09:28:01AM +0530, satya priya wrote:
> > > > > Add sleep pin ctrl for BT uart, and also change the bias
> > > > > configuration to match Bluetooth module.
> > > > >
> > > > > Signed-off-by: satya priya <[email protected]>
> > > > > ---
> > > > > Changes in V2:
> > > > > - This patch adds sleep state for BT UART. Newly added in V2.
> > > > >
> > > > > arch/arm64/boot/dts/qcom/sc7180-idp.dts | 42
> > > > > ++++++++++++++++++++++++++++-----
> > > > > 1 file changed, 36 insertions(+), 6 deletions(-)
> > > > >
> > > > > diff --git a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> > > > > b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> > > > > index 26cc491..bc919f2 100644
> > > > > --- a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> > > > > +++ b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> > > > > @@ -469,20 +469,50 @@
> > > > >
> > > > > &qup_uart3_default {
> > > > > pinconf-cts {
> > > > > - /*
> > > > > - * Configure a pull-down on 38 (CTS) to match the pull of
> > > > > - * the Bluetooth module.
> > > > > - */
> > > > > + /* Configure no pull on 38 (CTS) to match Bluetooth module */
> > > >
> > > > Has the pull from the Bluetooth module been removed or did the previous
> > > > config
> > > > incorrectly claim that the Bluetooth module has a pull-down?
> > > >
> > >
> > > The previous config was incorrect, so we corrected it to match the
> > > pull of
> > > BT.
> >
> > The pull config of the BT controller varies depending on its state,
> > could
> > you clarify which state you intend to match?
> >
>
> Since this line is driven by BT SoC, they could change their pull(although
> it's less likely). Recently on cherokee we worked with BT team and came to
> an agreement to keep no-pull from our side in order to not conflict with
> their pull in any state.
>
> > >
> > > > > pins = "gpio38";
> > > > > + bias-disable;
> > > > > + };
> > > > > +
> > > > > + pinconf-rts {
> > > > > + /* We'll drive 39 (RTS), so configure pull-down */
> > > > > + pins = "gpio39";
> > > > > + drive-strength = <2>;
> > > > > bias-pull-down;
> > > > > + };
> > > > > +
> > > > > + pinconf-tx {
> > > > > + /* We'll drive 40 (TX), so no pull */
> > > >
> > > > The rationales for RTS and TX contradict each other. According to the
> > > > comment
> > > > the reason to configure a pull-down on RTS is that it is driven by the
> > > > host.
> > > > Then for TX the reason to configure no pull is that it is driven by the
> > > > host.
> > > >
> > > > Please make sure the comments *really* describe the rationale, otherwise
> > > > they
> > > > are just confusing.
> > >
> > > The rationale for RTS is that we don't want it to be floating and
> > > want to
> > > make sure that it is pulled down, to receive bytes. Will modify the
> > > comment
> > > mentioning the same.
> >
> > Could you clarify what you mean with "to receive bytes"?
> >
>
> When we keep no-pull(floating), sometimes it may be pulled high and UART
> flow will be turned off(RFR_NOT_READY), due to this BT SoC wont be able to
> send data even though host is ready.
I'm a bit at a loss here, about two things:
RTS is an output pin controlled by the UART. IIUC if the UART port is active
and hardware flow control is enabled the RTS signal is either driven to high
or low, but not floating.
Now lets assume I'm wrong with the above and RTS can be floating. We only want
the BT SoC to send data when the host UART is ready to receive them, right?
RTS is an active low signal, hence by configuring it as a pull-down the BT
SoC can send data regardless of whether the host UART actually asserts RTS,
so the host UART may not be ready to receive it. I would argue that if there
is really such a thing as a floating RTS signal then it should have a pull-up,
to prevent the BT SoC from sending data at any time.
I'm not an expert in UART communication and pinconf, so it could be that I
got something wrong, but as of now it seems to me that no pull is the correct
config for RTS.