Re: [PATCH v2] PCI: apple: Follow the PCIe specifications when resetting the port
From: Luca Ceresoli
Date: Mon Nov 22 2021 - 16:32:25 EST
On 22/11/21 15:43, Marc Zyngier wrote:
> On Mon, 22 Nov 2021 12:03:47 +0000,
> Pali Rohár <pali@xxxxxxxxxx> wrote:
>> On Monday 22 November 2021 10:41:56 Marc Zyngier wrote:
>>> While the Apple PCIe driver works correctly when directly booted
>>> from the firmware, it fails to initialise when the kernel is booted
>>> from a bootloader using PCIe such as u-boot.
>>> That's beacuse we're missing a proper reset of the port (we only
>>> clear the reset, but never assert it).
>>> The PCIe spec requirements are two-fold:
>>> - #PERST must be asserted before setting up the clocks, and
>>> stay asserted for at least 100us (Tperst-clk).
>>> - Once #PERST is deasserted, the OS must wait for at least 100ms
>>> "from the end of a Conventional Reset" before we can start talking
>>> to the devices
>>> Implementing this results in a booting system.
>>> Fixes: 1e33888fbe44 ("PCI: apple: Add initial hardware bring-up")
>>> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
>>> Cc: Alyssa Rosenzweig <alyssa@xxxxxxxxxxxxx>
>>> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
>>> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>>> Cc: Pali Rohár <pali@xxxxxxxxxx>
>> Looks good, but see comment below.
>> Acked-by: Pali Rohár <pali@xxxxxxxxxx>
> Thanks for that.
>>> drivers/pci/controller/pcie-apple.c | 10 ++++++++++
>>> 1 file changed, 10 insertions(+)
>>> diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c
>>> index 1bf4d75b61be..957960a733c4 100644
>>> --- a/drivers/pci/controller/pcie-apple.c
>>> +++ b/drivers/pci/controller/pcie-apple.c
>>> @@ -539,13 +539,23 @@ static int apple_pcie_setup_port(struct apple_pcie *pcie,
>>> rmw_set(PORT_APPCLK_EN, port->base + PORT_APPCLK);
>>> + /* Engage #PERST before setting up the clock */
>>> + gpiod_set_value(reset, 0);
>>> ret = apple_pcie_setup_refclk(pcie, port);
>>> if (ret < 0)
>>> return ret;
>>> + /* The minimal Tperst-clk value is 100us (PCIe CMS r2.0, 2.6.2) */
>>> + usleep_range(100, 200);
>>> + /* Deassert #PERST */
>>> rmw_set(PORT_PERST_OFF, port->base + PORT_PERST);
>>> gpiod_set_value(reset, 1);
>> + Luca
>> Just one comment. PERST# (PCIe Reset) is active-low signal. De-asserting
>> means to really set value to 1.
>> But there was a discussion that de-asserting should be done by call:
>> gpiod_set_value(reset, 0);
>> Could we make this new pcie-apple.c driver to use gpiod_set_value(reset, 0)
>> for de-asserting, like in other drivers?
I agree it should be done right from the beginning since this is a new
driver. Fixing it later is a painful process.
> I guess it depends whether you care about the assertion or the signal
> itself. I think we may have a bug in the way the GPIOs are handled at
> the moment, as it makes no difference whether I register the GPIO are
> active high or active low...
> I guess that will be yet another thing to debug, but in the meantime
> we have a reliable reset.
Strange, in my case the "active low" pin polarity is correctly picked up
from device tree by the gpiolib code, thus using gpio_set_value(gpiod,
1) asserts the pin as it should, resulting in an electrically low pin.