[PATCH v2] PCI: rockchip: Add quirk to disable RC's ASPM L0s

[Rob Herring]

On Mon, Dec 12, 2016 at 07:51:27PM +0800, Shawn Lin wrote:
> Rockchip's RC outputs 100MHz reference clock but there are
> two methods for PHY to generate it.
> 
> (1)One of them is to use system PLL to generate 100MHz clock and
> the PHY will relock it and filter signal noise then outputs the
> reference clock.
> 
> (2)Another way is to share Soc's 24MHZ crystal oscillator with
> PHY and force PHY's DLL to generate 100MHz internally.
> 
> When using case(2), the exit from L0s doesn't work fine occasionally
> due to the broken design of RC receiver's logical circuit. So even if
> we use extended-synch, it still fails for PHY to relock the bits from
> FTS sometimes. This will hang the system.
> 
> Maybe we could argue that why not use case(1) to avoid it? The reason
> is that as we could see the reference clock is derived from system PLL
> and the path from it to PHY isn't so clean which means there are some
> noise introduced by power-domain and other buses can't be filterd out
> by PHY and we could see noise from the frequency spectrum by
> oscilloscope. This makes the TX compatibility test a little difficult
> to pass the spec. So case(1) and case(2) are both used indeed now. If
> using case(2), we should disable RC's L0s support, and that is why we
> need this property to indicate this quirk.
> 
> Also after checking quirk.c, I noticed there is already a quirk for
> disabling L0s unconditionally, quirk_disable_aspm_l0s. But obviously we
> shouldn't do that as mentioned above that case(1) could still works fine
> with L0s.
> 
> Reported-by: Jeffy Chen <jeffy.chen at rock-chips.com>
> Cc: Brian Norris <briannorris at chromium.org>
> Signed-off-by: Shawn Lin <shawn.lin at rock-chips.com>
> 
> ---
> 
> Changes in v2:
> - drop the quirk prefix
> 
>  Documentation/devicetree/bindings/pci/rockchip-pcie.txt | 2 ++
>  drivers/pci/host/pcie-rockchip.c                        | 9 +++++++++
>  2 files changed, 11 insertions(+)

Acked-by: Rob Herring <robh at kernel.org>