Hi,
On 31/05/21 7:24 pm, Luca Ceresoli wrote:
> Hi Pali,
>
> On 31/05/21 15:32, Pali Rohár wrote:
>> On Monday 31 May 2021 11:05:40 Luca Ceresoli wrote:
>>> The PCIe PERSTn reset pin is active low and should be asserted, then
>>> deasserted.
>>>
>>> The current implementation only drives the pin once in "HIGH" position,
>>> thus presumably it was intended to deassert the pin. This has two problems:
>>>
>>> 1) it assumes the pin was asserted by other means before loading the
>>> driver
>>> 2) it has the wrong polarity, since "HIGH" means "active", and the pin is
>>> presumably configured as active low coherently with the PCIe
>>> convention, thus it is driven physically to 0, keeping the device
>>> under reset unless the pin is configured as active high.
>>>
>>> Fix both problems by:
>>>
>>> 1) keeping devm_gpiod_get_optional(dev, NULL, GPIOD_OUT_HIGH) as is, but
>>> assuming the pin is correctly configured as "active low" this now
>>> becomes a reset assertion
>>> 2) adding gpiod_set_value(reset, 0) after a delay to deassert reset
>>>
>>> Fixes: 78bdcad05ea1 ("PCI: dra7xx: Add support to make GPIO drive PERST# line")
>>> Signed-off-by: Luca Ceresoli <luca@xxxxxxxxxxxxxxxx>
>>>
>>> ---
>>>
>>> Changes v1 -> v2:
>>> - No changes to the patch
>>> - Reword commit message according to suggestions from Bjorn Helgaas (from
>>> another patchset)
>>> - Add Fixes: tag
>>> ---
>>> drivers/pci/controller/dwc/pci-dra7xx.c | 2 ++
>>> 1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/pci/controller/dwc/pci-dra7xx.c b/drivers/pci/controller/dwc/pci-dra7xx.c
>>> index cb5d4c245ff6..11f392b7a9a2 100644
>>> --- a/drivers/pci/controller/dwc/pci-dra7xx.c
>>> +++ b/drivers/pci/controller/dwc/pci-dra7xx.c
>>> @@ -801,6 +801,8 @@ static int dra7xx_pcie_probe(struct platform_device *pdev)
>>> dev_err(&pdev->dev, "gpio request failed, ret %d\n", ret);
>>> goto err_gpio;
>>> }
>>> + usleep_range(1000, 2000);
>>
>> Hello! Just a note that this is again a new code pattern in another
>> driver for different wait value of PCIe Warm Reset timeout. I sent email
>> about these issues:
>> https://lore.kernel.org/linux-pci/20210310110535.zh4pnn4vpmvzwl5q@pali/
>>
>> Luca, how did you choose value 1000-2000 us? Do you have some reference
>> or specification which says that this value needs to be used?
>
> Sadly I haven't access to the PCIe specification.
>
> I'd be very happy to know what a correct value should be and update my
> patch.
I had given the timing mentioned in the specification here
https://lore.kernel.org/r/023c9b59-70bb-ed8d-a4c0-76eae726b574@xxxxxx
The PCI EXPRESS CARD ELECTROMECHANICAL SPECIFICATION defines the Power
Sequencing and Reset Signal Timings in Table 2-4. Please also refer Figure
2-10: Power Up of the CEM.
╔═════════════╤══════════════════════════════════════╤═════╤═════╤═══════╗
║ Symbol │ Parameter │ Min │ Max │ Units ║
╠═════════════╪══════════════════════════════════════╪═════╪═════╪═══════╣
║ T PVPERL │ Power stable to PERST# inactive │ 100 │ │ ms ║
╟─────────────┼──────────────────────────────────────┼─────┼─────┼───────╢
║ T PERST-CLK │ REFCLK stable before PERST# inactive │ 100 │ │ μs ║
╟─────────────┼──────────────────────────────────────┼─────┼─────┼───────╢
║ T PERST │ PERST# active time │ 100 │ │ μs ║
╟─────────────┼──────────────────────────────────────┼─────┼─────┼───────╢
║ T FAIL │ Power level invalid to PERST# active │ │ 500 │ ns ║
╟─────────────┼──────────────────────────────────────┼─────┼─────┼───────╢
║ T WKRF │ WAKE# rise – fall time │ │ 100 │ ns ║
╚═════════════╧══════════════════════════════════════╧═════╧═════╧═══════╝
The de-assertion of #PERST is w.r.t both power stable and refclk stable.
I'm yet to validate this patch, but IIRC devm_gpiod_get_optional(dev,
NULL, GPIOD_OUT_HIGH) will already de-assert the PERST line. Please note
the board here can have various combinations of NOT gate before the gpio
line is actually connected to the connector.
Thanks
Kishon
