PCI: dw-rockchip: Fix initial PERST# GPIO value

PATCH Applied Niklas Cassel 4 participants 4 messages Apr 17, 2024 – May 17, 2024

Subsystems (4)

Stable branch PCI Arm Rockchip PCI native host bridge and endpoint drivers

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Niklas Cassel

author

2024-04-17 16:42 UTC #0 lore raw

PATCH v3 1/1 PCI: dw-rockchip: Fix initial PERST# GPIO value

PERST# is active low according to the PCIe specification.

However, the existing pcie-dw-rockchip.c driver does:
gpiod_set_value(..., 0); msleep(100); gpiod_set_value(..., 1); When asserting + deasserting PERST#.

This is of course wrong, but because all the device trees for this compatible string have also incorrectly marked this GPIO as ACTIVE_HIGH:

$ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3568*
$ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3588*

The actual toggling of PERST# is correct.
(And we cannot change it anyway, since that would break device tree compatibility.)

However, this driver does request the GPIO to be initialized as GPIOD_OUT_HIGH, which does cause a silly sequence where PERST# gets toggled back and forth for no good reason.

Fix this by requesting the GPIO to be initialized as GPIOD_OUT_LOW (which for this driver means PERST# asserted).

This will avoid an unnecessary signal change where PERST# gets deasserted (by devm_gpiod_get_optional()) and then gets asserted
(by rockchip_pcie_start_link()) just a few instructions later.

Before patch, debug prints on EP side, when booting RC:

[  845.606810] pci: PERST# asserted by host!
[  852.483985] pci: PERST# de-asserted by host!
[  852.503041] pci: PERST# asserted by host!
[  852.610318] pci: PERST# de-asserted by host!

After patch, debug prints on EP side, when booting RC:

[  125.107921] pci: PERST# asserted by host!
[  132.111429] pci: PERST# de-asserted by host!

This extra, very short, PERST# assertion + deassertion has been reported to cause issues with certain WLAN controllers, e.g. RTL8822CE.

Fixes 0e898eb8df4e ("PCI: rockchip-dwc: Add Rockchip RK356X host controller driver")

Tested-by Jianfeng Liu <[email protected]>

Tested-by Heiko Stuebner <[email protected]>

Signed-off-by Niklas Cassel <[email protected]>

Reviewed-by Manivannan Sadhasivam <[email protected]>

Cc [email protected] # 5.15+

---
Changes since v2:
-Picked up tag from Heiko.
-Change subject (Bjorn).
-s/PERST/PERST#/ (Bjorn).

 drivers/pci/controller/dwc/pcie-dw-rockchip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

drivers/pci/controller/dwc/pcie-dw-rockchip.c +1 -1

index d6842141d384..a909e42b4273 100644
@@ -240,7 +240,7 @@ static int rockchip_pcie_resource_get(struct platform_device *pdev,
 		return PTR_ERR(rockchip->apb_base);
 
 	rockchip->rst_gpio = devm_gpiod_get_optional(&pdev->dev, "reset",
-						     GPIOD_OUT_HIGH);
+						     GPIOD_OUT_LOW);
 	if (IS_ERR(rockchip->rst_gpio))
 		return PTR_ERR(rockchip->rst_gpio);

Signature · 1 line

2.44.0

Heiko Stübner

maintainer Reviewed-by on v3 1/1

2024-04-30 08:38 UTC #1 lore raw

Am Mittwoch, 17. April 2024, 18:42:26 CEST schrieb Niklas Cassel:

Quoted 39 lines

PERST# is active low according to the PCIe specification.
However, the existing pcie-dw-rockchip.c driver does:
gpiod_set_value(..., 0); msleep(100); gpiod_set_value(..., 1); When asserting + deasserting PERST#.
This is of course wrong, but because all the device trees for this compatible string have also incorrectly marked this GPIO as ACTIVE_HIGH:
$ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3568*
$ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3588*
The actual toggling of PERST# is correct.
(And we cannot change it anyway, since that would break device tree compatibility.)
However, this driver does request the GPIO to be initialized as GPIOD_OUT_HIGH, which does cause a silly sequence where PERST# gets toggled back and forth for no good reason.
Fix this by requesting the GPIO to be initialized as GPIOD_OUT_LOW (which for this driver means PERST# asserted).
This will avoid an unnecessary signal change where PERST# gets deasserted (by devm_gpiod_get_optional()) and then gets asserted
(by rockchip_pcie_start_link()) just a few instructions later.
Before patch, debug prints on EP side, when booting RC:
[  845.606810] pci: PERST# asserted by host!
[  852.483985] pci: PERST# de-asserted by host!
[  852.503041] pci: PERST# asserted by host!
[  852.610318] pci: PERST# de-asserted by host!
After patch, debug prints on EP side, when booting RC:
[  125.107921] pci: PERST# asserted by host!
[  132.111429] pci: PERST# de-asserted by host!
This extra, very short, PERST# assertion + deassertion has been reported to cause issues with certain WLAN controllers, e.g. RTL8822CE.

Quoted 6 lines

Fixes 0e898eb8df4e ("PCI: rockchip-dwc: Add Rockchip RK356X host controller driver")
Tested-by Jianfeng Liu <[email protected]>
Tested-by Heiko Stuebner <[email protected]>
Signed-off-by Niklas Cassel <[email protected]>
Reviewed-by Manivannan Sadhasivam <[email protected]>
Cc [email protected] # 5.15+

Reviewed-by Heiko Stuebner <[email protected]>

it also matches what the vendor kernel does.

Bjorn Helgaas

2024-05-15 21:20 UTC #2 lore raw

In reply to Niklas Cassel

Quoted 39 lines · Niklas Cassel

PERST# is active low according to the PCIe specification.
However, the existing pcie-dw-rockchip.c driver does:
gpiod_set_value(..., 0); msleep(100); gpiod_set_value(..., 1); When asserting + deasserting PERST#.
This is of course wrong, but because all the device trees for this compatible string have also incorrectly marked this GPIO as ACTIVE_HIGH:
$ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3568*
$ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3588*
The actual toggling of PERST# is correct.
(And we cannot change it anyway, since that would break device tree compatibility.)
However, this driver does request the GPIO to be initialized as GPIOD_OUT_HIGH, which does cause a silly sequence where PERST# gets toggled back and forth for no good reason.
Fix this by requesting the GPIO to be initialized as GPIOD_OUT_LOW (which for this driver means PERST# asserted).
This will avoid an unnecessary signal change where PERST# gets deasserted (by devm_gpiod_get_optional()) and then gets asserted
(by rockchip_pcie_start_link()) just a few instructions later.
Before patch, debug prints on EP side, when booting RC:
[  845.606810] pci: PERST# asserted by host!
[  852.483985] pci: PERST# de-asserted by host!
[  852.503041] pci: PERST# asserted by host!
[  852.610318] pci: PERST# de-asserted by host!
After patch, debug prints on EP side, when booting RC:
[  125.107921] pci: PERST# asserted by host!
[  132.111429] pci: PERST# de-asserted by host!
This extra, very short, PERST# assertion + deassertion has been reported to cause issues with certain WLAN controllers, e.g. RTL8822CE.

Quoted 6 lines

Fixes 0e898eb8df4e ("PCI: rockchip-dwc: Add Rockchip RK356X host controller driver")
Tested-by Jianfeng Liu <[email protected]>
Tested-by Heiko Stuebner <[email protected]>
Signed-off-by Niklas Cassel <[email protected]>
Reviewed-by Manivannan Sadhasivam <[email protected]>
Cc [email protected] # 5.15+

Applied by Krzysztof to pci/controller/rockchip. His outgoing mail queue was stuck, but I'm trying to squeeze this into v6.10.

Quoted 25 lines

---
Changes since v2:

(quoted diff) +0 -3

-Picked up tag from Heiko.
-Change subject (Bjorn).
-s/PERST/PERST#/ (Bjorn).
 
 drivers/pci/controller/dwc/pcie-dw-rockchip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

drivers/pci/controller/dwc/pcie-dw-rockchip.c +1 -1

index d6842141d384..a909e42b4273 100644
@@ -240,7 +240,7 @@ static int rockchip_pcie_resource_get(struct platform_device *pdev,
 		return PTR_ERR(rockchip->apb_base);
 
 	rockchip->rst_gpio = devm_gpiod_get_optional(&pdev->dev, "reset",
-						     GPIOD_OUT_HIGH);
+						     GPIOD_OUT_LOW);
 	if (IS_ERR(rockchip->rst_gpio))
 		return PTR_ERR(rockchip->rst_gpio);

Signature · 1 line

2.44.0

Krzysztof Wilczyński

Applied

2024-05-17 11:22 UTC #3 lore raw

In reply to Niklas Cassel

Hello,

Quoted 32 lines

PERST# is active low according to the PCIe specification.
However, the existing pcie-dw-rockchip.c driver does:
gpiod_set_value(..., 0); msleep(100); gpiod_set_value(..., 1); When asserting + deasserting PERST#.
This is of course wrong, but because all the device trees for this compatible string have also incorrectly marked this GPIO as ACTIVE_HIGH:
$ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3568*
$ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3588*
The actual toggling of PERST# is correct.
(And we cannot change it anyway, since that would break device tree compatibility.)
However, this driver does request the GPIO to be initialized as GPIOD_OUT_HIGH, which does cause a silly sequence where PERST# gets toggled back and forth for no good reason.
Fix this by requesting the GPIO to be initialized as GPIOD_OUT_LOW (which for this driver means PERST# asserted).
This will avoid an unnecessary signal change where PERST# gets deasserted (by devm_gpiod_get_optional()) and then gets asserted
(by rockchip_pcie_start_link()) just a few instructions later.
Before patch, debug prints on EP side, when booting RC:
[  845.606810] pci: PERST# asserted by host!
[  852.483985] pci: PERST# de-asserted by host!
[  852.503041] pci: PERST# asserted by host!
[  852.610318] pci: PERST# de-asserted by host!

Quoted 6 lines

After patch, debug prints on EP side, when booting RC:
[  125.107921] pci: PERST# asserted by host!
[  132.111429] pci: PERST# de-asserted by host!
This extra, very short, PERST# assertion + deassertion has been reported to cause issues with certain WLAN controllers, e.g. RTL8822CE.

Applied to controller/rockchip, thank you!

[1/1] PCI: dw-rockchip: Fix initial PERST# GPIO value

      https://git.kernel.org/pci/pci/c/b00c483a1075

	Krzysztof