On 2024-06-12 19:47, Dmitry Torokhov wrote:
Hi Marton,
Hi Dmitry,
On Fri, Jun 07, 2024 at 11:04:00AM +0200, Martin Schiller wrote:
Commit 90c2d2eb7ab5 ("MIPS: pci: lantiq: switch to using gpiod API")
not
only switched to the gpiod API, but also inverted / changed the
polarity
of the GPIO.
According to the PCI specification, the RST# pin is an active-low
signal. However, most of the device trees that have been widely used
for
a long time (mainly in the openWrt project) define this GPIO as
active-high and the old driver code inverted the signal internally.
Apparently there are actually boards where the reset gpio must be
operated inverted. For this reason, we cannot use the
GPIOD_OUT_LOW/HIGH
flag for initialization. Instead, we must explicitly set the gpio to
value 1 in order to take into account any "GPIO_ACTIVE_LOW" flag that
may have been set.
Do you have example of such boards? They could not have worked before
90c2d2eb7ab5 because it was actively setting the reset line to physical
high, which should leave the device in reset state if there is an
inverter between the AP and the device.
Oh, you're right. I totally missed that '__gpio_set_value' was used in
the original code and that raw accesses took place without paying
attention to the GPIO_ACTIVE_* flags.
You can find the device trees I am talking about in [1].
@Thomas Bogendoerfer:
Would it be possible to stop the merging of this patch?
I think We have to do do some further/other changes.
In order to remain compatible with all these existing device trees, we
should therefore keep the logic as it was before the commit.
With gpiod API operating with logical states there's still difference
in
logic:
gpiod_set_value_cansleep(reset_gpio, 1);
will leave GPIO at 1 if it is described as GPIO_ACTIVE_HIGH (which is
apparently what you want for boards with broken DTS) but for boards
that accurately describe GPIO as GPIO_ACTIVE_LOW it well drive GPIO to
0, leaving the card in reset state.
You should either use gpiod_set_raw_value_calsleep() or we can try and
quirk it in gpiolib (like we do for many other cases of incorrect GPIO
polarity descriptions and which is my preference).
This still leaves the question about boards that require inversion. Are
you saying that they have real signal inverter on the line or that
their
device trees correctly describe the signal as GPIO_ACTIVE_LOW?
BTW, please consider getting DTS trees for your devices into mainline.
Why do you keep them separate?
Unfortunately, these are not "my" devices and I can't even test them.
I've got feedback from some users when I updated the lantiq target to
linux 6.1 in openwrt.
Let's assume that all boards physically expect an active-low signal.
If the GPIO_ACTIVE_LOW flag were now set in the device tree, the
original (old) driver would have an incorrect initial level (LOW instead
of HIGH) due to the
gpio_direction_output(reset_gpio, 1);
This is probably the reason why the flag GPIO_ACTIVE_HIGH is set in
almost all dts files in openwrt.
But with commit 90c2d2eb7ab5 the initial level (LOW) is guaranteed to be
wrong because of the "GPIOD_OUT_LOW" and cannot be changed by "wrong"
device tree settings.
The signal curve is LOW -> LOW -> HIGH instead of HIGH -> LOW -> HIGH.
Fixes: 90c2d2eb7ab5 ("MIPS: pci: lantiq: switch to using gpiod API")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Martin Schiller <ms@xxxxxxxxxx>
---
arch/mips/pci/pci-lantiq.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/mips/pci/pci-lantiq.c b/arch/mips/pci/pci-lantiq.c
index 68a8cefed420..0844db34022e 100644
--- a/arch/mips/pci/pci-lantiq.c
+++ b/arch/mips/pci/pci-lantiq.c
@@ -124,14 +124,14 @@ static int ltq_pci_startup(struct
platform_device *pdev)
clk_disable(clk_external);
/* setup reset gpio used by pci */
- reset_gpio = devm_gpiod_get_optional(&pdev->dev, "reset",
- GPIOD_OUT_LOW);
+ reset_gpio = devm_gpiod_get_optional(&pdev->dev, "reset",
GPIOD_ASIS);
error = PTR_ERR_OR_ZERO(reset_gpio);
if (error) {
dev_err(&pdev->dev, "failed to request gpio: %d\n", error);
return error;
}
gpiod_set_consumer_name(reset_gpio, "pci_reset");
+ gpiod_direction_output(reset_gpio, 1);
/* enable auto-switching between PCI and EBU */
ltq_pci_w32(0xa, PCI_CR_CLK_CTRL);
@@ -194,10 +194,10 @@ static int ltq_pci_startup(struct
platform_device *pdev)
/* toggle reset pin */
if (reset_gpio) {
- gpiod_set_value_cansleep(reset_gpio, 1);
+ gpiod_set_value_cansleep(reset_gpio, 0);
wmb();
mdelay(1);
- gpiod_set_value_cansleep(reset_gpio, 0);
+ gpiod_set_value_cansleep(reset_gpio, 1);
}
return 0;
}
--
2.39.2
Thanks.
[1]
https://git.openwrt.org/?p=openwrt/openwrt.git;a=tree;f=target/linux/lantiq/files/arch/mips/boot/dts/lantiq
