回复: 回复: [PATCH v4 4/4] PCI: mediatek-gen3: Add Airoha EN7581 support

[Hui Ma (马慧)]

> On Fri, Nov 08, 2024 at 01:23:35AM +0000, Hui Ma (马慧) wrote:
> > > On Thu, Nov 07, 2024 at 05:21:45PM +0100, Lorenzo Bianconi wrote:
> > > > On Nov 07, Bjorn Helgaas wrote:
> > > > > On Thu, Nov 07, 2024 at 08:39:43AM +0100, Lorenzo Bianconi wrote:
> > > > > > > On Wed, Nov 06, 2024 at 11:40:28PM +0100, Lorenzo Bianconi wrote:
> > > > > > > > > On Wed, Jul 03, 2024 at 06:12:44PM +0200, Lorenzo Bianconi wrote:
> > > > > > > > > > Introduce support for Airoha EN7581 PCIe controller 
> > > > > > > > > > to
> > > > > > > > > > mediatek-gen3 PCIe controller driver.
> > > > > > > > > > ...
> > > > > 
> > > > > > > > > Is this where PERST# is asserted?  If so, a comment to 
> > > > > > > > > that effect would be helpful.  Where is PERST# deasserted?
> > > > > > > > > Where are the required delays before deassert done?
> > > > > > > > 
> > > > > > > > I can add a comment in en7581_pci_enable() describing 
> > > > > > > > the PERST issue for EN7581. Please note we have a 250ms 
> > > > > > > > delay in
> > > > > > > > en7581_pci_enable() after configuring REG_PCI_CONTROL register.
> > > > > > > > 
> > > > > > > > https://github.com/torvalds/linux/blob/master/drivers/cl
> > > > > > > > k/cl
> > > > > > > > k-en7523.c#L396
> > > > > > > 
> > > > > > > Does that 250ms delay correspond to a PCIe mandatory 
> > > > > > > delay, e.g., something like PCIE_T_PVPERL_MS?  I think it 
> > > > > > > would be nice to have the required PCI delays in this 
> > > > > > > driver if possible so it's easy to verify that they are all covered.
> > > > > > 
> > > > > > IIRC I just used the delay value used in the vendor sdk. I 
> > > > > > do not have a strong opinion about it but I guess if we move 
> > > > > > it in the pcie-mediatek-gen3 driver, we will need to add it 
> > > > > > in each driver where this clock is used. What do you think?
> > > > > 
> > > > > I don't know what the 250ms delay is for.  If it is for a 
> > > > > required PCI delay, we should use the relevant standard 
> > > > > #define for it, and it should be in the PCI controller driver.  
> > > > > Otherwise it's impossible to verify that all the drivers are doing the correct delays.
> > > > 
> > > > ack, fine to me. Do you prefer to keep 250ms after
> > > > clk_bulk_prepare_enable() in mtk_pcie_en7581_power_up() or just use PCIE_T_PVPERL_MS (100)?
> > > > I can check if 100ms works properly.
> > > 
> > > It's not clear to me where the relevant events are for these chips.
> > > 
> > > Do you have access to the PCIe CEM spec?  The diagram in r6.0, sec 
> > > 2.2.1, is helpful.  It shows the required timings for Power 
> > > Stable, REFCLK Stable, PERST# deassert, etc.
> > > 
> > > Per sec 2.11.2, PERST# must be asserted for at least 100us 
> > > (T_PERST), PERST# must be asserted for at least 100ms after Power 
> > > Stable (T_PVPERL), and PERST# must be asserted for at least 100us 
> > > after REFCLK Stable.
> > > 
> > > It would be helpful if we could tell by reading the source where 
> > > some of these critical events happen, and that the relevant delays 
> > > are there.  For example, if PERST# is asserted/deasserted by 
> > > "clk_enable()" or similar, it's not at all obvious from the code, 
> > > so we should have a comment to that effect.
> > 
> > >I reviewed the vendor sdk and it just do something like in clk_enable():
> > >
> > >	...
> > >	val = readl(0x88);
> > >	writel(val | BIT(16) | BIT(29) | BIT(26), 0x88);
> > >	/*wait link up*/
> > >	mdelay(1000);
> > >	...
> > >
> > >@Hui.Ma: is it fine use msleep(100) (so PCIE_T_PVPERL_MS) instead 
> > >of msleep(1000) (so PCIE_LINK_RETRAIN_TIMEOUT_MS)?
> >
> > 	I think msleep(1000) will be safer, because some device won't
> > 	link up with msleep(100).
>> 
>> Do you have details about this?  I guess it only hurts mediatek, but 
>> increasing the minimum time to bring up a PCI hierarchy by almost an 
>> entire second is a pretty big deal.
>> 
>> If this delay corresponds to the required T_PVPERL delay and 100ms 
>> isn't enough for some endpoints, those endpoints should fail with many 
>> host controllers, not just mediatek, so I would suspect the mediatek 
>> controller or a certain platform, not the endpoint itself.
>> 
>> If this corresponds to T_PVPERL and mediatek needs longer, I would 
>> document that by using "PCIE_T_PVPERL_MS * 10" and adding a comment 
>> about why (affected platform/device, hardware erratum, etc).
>> 
>> Bottom line, I don't really care what the value is, but I *would* like 
>> to be able to read pcie-mediatek-gen3.c and see the point where PCI 
>> power is stable, a delay of at least T_PVPERL, and where PERST# is 
>> deasserted because that's the main timing requirement on software.

>>I run some testes using 100ms delay (PCIE_T_PVPERL_MS) after
>>clk_bulk_prepare_enable() in mtk_pcie_en7581_power_up() and it works fine for me (I tested with a MT7915 WiFi PCIe nic connected to the PCIe sock).
>>Moreover, we already poll PCIE_LINK_STATUS_REG register to check the link status in mtk_pcie_startup_port(), right? I guess we can proceed with 100ms delay in mtk_pcie_en7581_power_up().
Yes.

Hi Lorenzo/Bjorn，
	After our internal discussion and tests, we confirmed that a 100ms delay is enough.



Regards,
Hui

>Regards,
>Lorenzo

> 
> Bjorn