Re: Re: [PATCH 1/3] dt-bindings: imx6q-pcie: specify the imx8mq pcie phy voltage

Hi Richard,

Am Montag, dem 22.03.2021 um 09:06 +0000 schrieb Richard Zhu:

quoted

-----Original Message-----
From: Lucas Stach <l.stach@pengutronix.de>
Sent: Friday, March 19, 2021 5:49 PM
To: Richard Zhu <hongxing.zhu@nxp.com>; andrew.smirnov@gmail.com;
shawnguo@kernel.org; kw@linux.com; bhelgaas@google.com;
stefan@agner.ch; lorenzo.pieralisi@arm.com
Cc: linux-pci@vger.kernel.org; dl-linux-imx <redacted>;
linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
kernel@pengutronix.de
Subject: [EXT] Re: [PATCH 1/3] dt-bindings: imx6q-pcie: specify the
imx8mq
pcie phy voltage
Am Freitag, dem 19.03.2021 um 16:24 +0800 schrieb Richard Zhu:

quoted

Both 1.8v and 3.3v power supplies can be feeded to i.MX8MQ PCIe
PHY.
In default, the PCIE_VPH voltage is suggested to be 1.8v refer to
data
sheet. When PCIE_VPH is supplied by 3.3v in the HW schematic
design,
the VREG_BYPASS bits of GPR registers should be cleared from
default
value 1b'1 to 1b'0.

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
---
 Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt | 4
++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/devicetree/bindings/pci/fsl,imx6q-

pcie.txt
b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt
index de4b2baf91e8..23efbad9e804 100644

--- a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt
+++ b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt

@@ -59,6 +59,10 @@ Additional required properties for imx7d-pcie

and

imx8mq-pcie:

quoted

 Additional required properties for imx8mq-pcie:
 - clock-names: Must include the following additional entries:
      - "pcie_aux"
+- pcie-vph-3v3: If present then PCIE_VPH is feeded by 3.3v in
the HW
+  schematic design. The PCIE_VPH is suggested to be 1.8v refer
to the
+  data sheet. If the PCIE_VPH is supplied by 3.3V, the
VREG_BYPASS
+  should be cleared to zero accordingly.

Uhm, no. Please don't add boolean DT properties for random parts of
the
board design.

If we need to know the voltage of PCIE_VPH, we should really add
the VPH
regulator as a supply to the PCIe controller node, then work out
the voltage
the usual way by using the Linux regulator API.

[Richard Zhu] Hi Lucas:
Thanks for your comments. Since the vgen5_reg is used to power up
PCIe PHY on i.MX8MQ EVK board,
 and it's set to be "regulator-always-on;".
Did only the regulator_get_voltage or combined with
regulator_enable/regulator_disable can be used in the driver?

The regulator API doesn't care, you can call enable/disable in the
driver as normal. If the regulator is marked as always-on it will just
stay enabled even if the use-count drops to 0.

The other question however is if it's even allowed by the SoC design to
disable this supply outside of deep power down. A quick look into the
reference manual and datasheet didn't yield any information about this.

Regards,
Lucas


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