[RESEND PATCH 2/2] PCI: rockchip: Add quirk to disable RC's ASPM L0s
robh at kernel.org
Tue Nov 15 14:26:49 PST 2016
On Mon, Nov 14, 2016 at 12:11:06PM +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.
Doesn't the driver know which case it is using? I don't see why you need
the quirk property.
> 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.
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