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

[Hui Ma (马慧)]

> 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/clk/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)?
Hi Lorenzo，
	I think msleep(1000) will be safer,because some device won't link up with msleep(100).
Regards,
Hui
>
>Regards,
>Lorenzo

> 
> Bjorn