Re: [PATCH 2/4] Bluetooth: hci_qca: Don't vote for specific voltage

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Hi Matthias,

On 2019-10-22 22:45, Matthias Kaehlcke wrote:
On Tue, Oct 22, 2019 at 11:35:43AM +0530, Balakrishna Godavarthi wrote:
Hi Matthias, Bjorn andresson,

On 2019-10-21 12:07, Harish Bandi wrote:
> + Bala
>
> On 2019-10-18 23:52, Matthias Kaehlcke wrote:
> > On Thu, Oct 17, 2019 at 10:24:02PM -0700, Bjorn Andersson wrote:
> > > Devices with specific voltage requirements should not request voltage
> > > from the driver, but instead rely on the system configuration to
> > > define
> > > appropriate voltages for each rail.
> > >
> > > This ensures that PMIC and board variations are accounted for,
> > > something
> > > that the 0.1V range in the hci_qca driver currently tries to address.
> > > But on the Lenovo Yoga C630 (with wcn3990) vddch0 is 3.1V, which
> > > means
> > > the driver will fail to set the voltage.
> > >
> > > Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
> > > ---
> > >  drivers/bluetooth/hci_qca.c | 26 ++++++++------------------
> > >  1 file changed, 8 insertions(+), 18 deletions(-)
> > >
> > > diff --git a/drivers/bluetooth/hci_qca.c
> > > b/drivers/bluetooth/hci_qca.c
> > > index c07c529b0d81..54aafcc69d06 100644
> > > --- a/drivers/bluetooth/hci_qca.c
> > > +++ b/drivers/bluetooth/hci_qca.c
> > > @@ -130,8 +130,6 @@ enum qca_speed_type {
> > >   */
> > >  struct qca_vreg {
> > >  	const char *name;
> > > -	unsigned int min_uV;
> > > -	unsigned int max_uV;
> > >  	unsigned int load_uA;
> > >  };
> > >
> > > @@ -1332,10 +1330,10 @@ static const struct hci_uart_proto
> > > qca_proto = {
> > >  static const struct qca_vreg_data qca_soc_data_wcn3990 = {
> > >  	.soc_type = QCA_WCN3990,
> > >  	.vregs = (struct qca_vreg []) {
> > > -		{ "vddio",   1800000, 1900000,  15000  },
> > > -		{ "vddxo",   1800000, 1900000,  80000  },
> > > -		{ "vddrf",   1300000, 1350000,  300000 },
> > > -		{ "vddch0",  3300000, 3400000,  450000 },
> > > +		{ "vddio", 15000  },
> > > +		{ "vddxo", 80000  },
> > > +		{ "vddrf", 300000 },
> > > +		{ "vddch0", 450000 },
> > >  	},
> > >  	.num_vregs = 4,
> > >  };
> > > @@ -1343,10 +1341,10 @@ static const struct qca_vreg_data
> > > qca_soc_data_wcn3990 = {
> > >  static const struct qca_vreg_data qca_soc_data_wcn3998 = {
> > >  	.soc_type = QCA_WCN3998,
> > >  	.vregs = (struct qca_vreg []) {
> > > -		{ "vddio",   1800000, 1900000,  10000  },
> > > -		{ "vddxo",   1800000, 1900000,  80000  },
> > > -		{ "vddrf",   1300000, 1352000,  300000 },
> > > -		{ "vddch0",  3300000, 3300000,  450000 },
> > > +		{ "vddio", 10000  },
> > > +		{ "vddxo", 80000  },
> > > +		{ "vddrf", 300000 },
> > > +		{ "vddch0", 450000 },
> > >  	},
> > >  	.num_vregs = 4,
> > >  };
> > > @@ -1386,13 +1384,6 @@ static int qca_power_off(struct hci_dev *hdev)
> > >  static int qca_enable_regulator(struct qca_vreg vregs,
> > >  				struct regulator *regulator)
> > >  {
> > > -	int ret;
> > > -
> > > -	ret = regulator_set_voltage(regulator, vregs.min_uV,
> > > -				    vregs.max_uV);
> > > -	if (ret)
> > > -		return ret;
> > > -
> > >  	return regulator_enable(regulator);
> > >
> > >  }
> > > @@ -1401,7 +1392,6 @@ static void qca_disable_regulator(struct
> > > qca_vreg vregs,
> > >  				  struct regulator *regulator)
> > >  {
> > >  	regulator_disable(regulator);
> > > -	regulator_set_voltage(regulator, 0, vregs.max_uV);
> > >
> > >  }
> >
> > This was brought up multiple times during the initial review, but
> > wasn't addressed.
> >
> > Reviewed-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>


yes true PMIC dts regulator should do this.
But we have some real time issues observed.

Issue 1:

In PMIC dts node, ASAIK we have three levels of voltages.

1. Default voltage.
2. Minimum voltage. (mandatory entry)
3. Maximum voltage. (mandatory entry)

Let us assume that the if PMIC regulator dts node supports defaults voltage
to 3.2 Volts and Min  as 3.1 V and max as 3.3V
So default operating voltage is 3.1V when we turn on BT (but according to
spec SoC requires min of 3.3V to operate,
Might have some functionality failures on end to end testing

The PMIC regulator shouldn't be configured with the entire range of voltages it can generate, but with a range of voltages that is suitable for all its
consumers.

In other words if BT requires a minimum voltage of 3.3V the minimum voltage
of the regulator should be at least 3.3V.

Issue 2:

WCN3990 RF is shared with WiFi, so it also try to turn on the regulators. Wifi driver uses the same approach of restricting to min and max voltages in
driver.
Let us assume we turned ON BT and CH0 is set to 3.1v (as in your case), Wifi is tuned on now, as its request the CH0 to operate at 3.3 Volts, regulator
will fail to set this voltage as BT is operating
at CH0 3.1v (assuming max voltage is 3.2v)
https://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git/tree/drivers/net/wireless/ath/ath10k/snoc.c#n39

see above

Issue 3:

By mistake PMIC has low min or default voltage and high max voltages, that
is harm for WNC3990.

I would suggest to restrict the min and max voltages in driver, instead of
relaying on PMIC to do this.
BTW pmic will do this and doing it in our driver is safer.

What if another device switches the regulator on before BT?

Again, what you describe is a misconfiguration of the regulator and should be fixed at its root, instead of implementing unreliable 'safeguards' in each
and every driver using regulators.

Thanks for detail analysis :)
--
Regards
Balakrishna.



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