Re: [PATCH v1 8/9] PCI: PLDA: starfive: Add JH7110 PCIe controller

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, Jul 24, 2023 at 06:48:47PM +0800, Kevin Xie wrote:
> On 2023/7/21 0:15, Bjorn Helgaas wrote:
> > On Thu, Jul 20, 2023 at 06:11:59PM +0800, Kevin Xie wrote:
> >> On 2023/7/20 0:48, Bjorn Helgaas wrote:
> >> > On Wed, Jul 19, 2023 at 06:20:56PM +0800, Minda Chen wrote:
> >> >> Add StarFive JH7110 SoC PCIe controller platform
> >> >> driver codes.

> >> However, in the compatibility testing with several NVMe SSD, we
> >> found that Lenovo Thinklife ST8000 NVMe can not get ready in 100ms,
> >> and it actually needs almost 200ms.  Thus, we increased the T_PVPERL
> >> value to 300ms for the better device compatibility.
> > ...
> > 
> > Thanks for this valuable information!  This NVMe issue potentially
> > affects many similar drivers, and we may need a more generic fix so
> > this device works well with all of them.
> > 
> > T_PVPERL is defined to start when power is stable.  Do you have a way
> > to accurately determine that point?  I'm guessing this:
> > 
> >   gpiod_set_value_cansleep(pcie->power_gpio, 1)
> > 
> > turns the power on?  But of course that doesn't mean it is instantly
> > stable.  Maybe your testing is telling you that your driver should
> > have a hardware-specific 200ms delay to wait for power to become
> > stable, followed by the standard 100ms for T_PVPERL?
> 
> You are right, we did not take the power stable cost into account.
> T_PVPERL is enough for Lenovo Thinklife ST8000 NVMe SSD to get ready,
> and the extra cost is from the power circuit of a PCIe to M.2 connector,
> which is used to verify M.2 SSD with our EVB at early stage.

Hmm.  That sounds potentially interesting.  I assume you're talking
about something like this: https://www.amazon.com/dp/B07JKH5VTL

I'm not familiar with the timing requirements for something like this.
There is a PCIe M.2 spec with some timing requirements, but I don't
know whether or how software is supposed to manage this.  There is a
T_PVPGL (power valid to PERST# inactive) parameter, but it's
implementation specific, so I don't know what the point of that is.
And I don't see a way for software to even detect the presence of such
an adapter.

But I assume some end users will use adapters like this and expect it
to "just work," so it would be nice if it did.

> As the Thinklife NVMe SSD may be a halted product, and the onboard
> power circuit of VisionFive V2 is no problem, we decided revert the
> sleep time to be 100ms.

Even though the product may be end-of-life, people will probably still
try to use it, and I would like it to work.  Otherwise we end up with
frustrated users and problem reports that are hard to resolve.  But I
don't know where to go here.

Bjorn