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

[Lorenzo Bianconi <lorenzo@kernel.org>]

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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/clk-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.

Regards,
Lorenzo

> 
> I don't know what other drivers are using that clock.  Are you
> suggesting that it may be used in non-PCI situations where the
> required delay might be different?  If another user requires 250ms,
> but PCI requires only 100ms, I think it would be worth having separate
> delays in each user so PCI wouldn't have to pay that extra 150ms.
> 
> Bjorn

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