[PATCH v3] PCI: dw-rockchip: Fix initial PERST# GPIO value

[PATCH v3] PCI: dw-rockchip: Fix initial PERST# GPIO value

[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.

Fixes: 0e898eb8df4e ("PCI: rockchip-dwc: Add Rockchip RK356X host controller driver")
Tested-by: Jianfeng Liu <liujianfeng1994@gmail.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: stable@vger.kernel.org	# 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(-)

diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
index d6842141d384..a909e42b4273 100644
--- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
+++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
@@ -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);
 
-- 
2.44.0


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Re: [PATCH v3] PCI: dw-rockchip: Fix initial PERST# GPIO value

[Heiko Stübner]

Am Mittwoch, 17. April 2024, 18:42:26 CEST schrieb 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.
> 
> Fixes: 0e898eb8df4e ("PCI: rockchip-dwc: Add Rockchip RK356X host controller driver")
> Tested-by: Jianfeng Liu <liujianfeng1994@gmail.com>
> Tested-by: Heiko Stuebner <heiko@sntech.de>
> Signed-off-by: Niklas Cassel <cassel@kernel.org>
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> Cc: stable@vger.kernel.org	# 5.15+

Reviewed-by: Heiko Stuebner <heiko@sntech.de>

it also matches what the vendor kernel does.



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Re: [PATCH v3] PCI: dw-rockchip: Fix initial PERST# GPIO value

[Bjorn Helgaas]

On Wed, Apr 17, 2024 at 06:42:26PM +0200, Niklas Cassel wrote:
> 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 <liujianfeng1994@gmail.com>
> Tested-by: Heiko Stuebner <heiko@sntech.de>
> Signed-off-by: Niklas Cassel <cassel@kernel.org>
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> Cc: stable@vger.kernel.org	# 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.

> ---
> 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(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
> index d6842141d384..a909e42b4273 100644
> --- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
> +++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
> @@ -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);
>  
> -- 
> 2.44.0
> 

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Re: [PATCH v3] PCI: dw-rockchip: Fix initial PERST# GPIO value

[Krzysztof Wilczyński]

Hello,

> 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.

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

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