Re: [PATCH v5 2/2] misc: rtsx: Add power saving functions and fix driving parameter

From: Bjorn Helgaas
Date: Tue Sep 15 2020 - 12:22:54 EST

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In reply to: 吳昊澄 Ricky: "RE: [PATCH v5 2/2] misc: rtsx: Add power saving functions and fix driving parameter"
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On Tue, Sep 15, 2020 at 08:24:50AM +0000, 吳昊澄 Ricky wrote:
> > -----Original Message-----
> > From: Bjorn Helgaas [mailto:helgaas@xxxxxxxxxx]
> > Sent: Friday, September 11, 2020 10:56 PM
> > To: 吳昊澄 Ricky
> > Cc: arnd@xxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; bhelgaas@xxxxxxxxxx;
> > ulf.hansson@xxxxxxxxxx; rui_feng@xxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > puranjay12@xxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
> > vailbhavgupta40@xxxxxxxxxx
> > Subject: Re: [PATCH v5 2/2] misc: rtsx: Add power saving functions and fix driving
> > parameter
> >
> > On Fri, Sep 11, 2020 at 08:18:22AM +0000, 吳昊澄 Ricky wrote:
> > > > -----Original Message-----
> > > > From: Bjorn Helgaas [mailto:helgaas@xxxxxxxxxx]
> > > > Sent: Thursday, September 10, 2020 1:44 AM
> > > > To: 吳昊澄 Ricky
> > > > Cc: arnd@xxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; bhelgaas@xxxxxxxxxx;
> > > > ulf.hansson@xxxxxxxxxx; rui_feng@xxxxxxxxxxxxxx;
> > linux-kernel@xxxxxxxxxxxxxxx;
> > > > puranjay12@xxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
> > > > vailbhavgupta40@xxxxxxxxxx
> > > > Subject: Re: [PATCH v5 2/2] misc: rtsx: Add power saving functions and fix
> > driving
> > > > parameter
> > > >
> > > > On Wed, Sep 09, 2020 at 07:10:19AM +0000, 吳昊澄 Ricky wrote:
> > > > > > -----Original Message-----
> > > > > > From: Bjorn Helgaas [mailto:helgaas@xxxxxxxxxx]
> > > > > > Sent: Wednesday, September 09, 2020 6:29 AM
> > > > > > To: 吳昊澄 Ricky
> > > > > > Cc: arnd@xxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx;
> > bhelgaas@xxxxxxxxxx;
> > > > > > ulf.hansson@xxxxxxxxxx; rui_feng@xxxxxxxxxxxxxx;
> > > > linux-kernel@xxxxxxxxxxxxxxx;
> > > > > > puranjay12@xxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
> > > > > > vailbhavgupta40@xxxxxxxxxx
> > > > > > Subject: Re: [PATCH v5 2/2] misc: rtsx: Add power saving functions and fix
> > > > driving
> > > > > > parameter
> > > > > >
> > > > > > On Mon, Sep 07, 2020 at 06:07:31PM +0800, ricky_wu@xxxxxxxxxxx
> > wrote:
> > > > > > > From: Ricky Wu <ricky_wu@xxxxxxxxxxx>
> > > > > > >
> > > > > > > v4:
> > > > > > > split power down flow and power saving function to two patch
> > > > > > >
> > > > > > > v5:
> > > > > > > fix up modified change under the --- line
> > > > > >
> > > > > > Hehe, this came out *above* the "---" line :)
> > > > > >
> > > > > > > Add rts522a L1 sub-state support
> > > > > > > Save more power on rts5227 rts5249 rts525a rts5260
> > > > > > > Fix rts5260 driving parameter
> > > > > > >
> > > > > > > Signed-off-by: Ricky Wu <ricky_wu@xxxxxxxxxxx>
> > > > > > > ---
> > > > > > > drivers/misc/cardreader/rts5227.c | 112 +++++++++++++++++++++-
> > > > > > > drivers/misc/cardreader/rts5249.c | 145
> > > > > > ++++++++++++++++++++++++++++-
> > > > > > > drivers/misc/cardreader/rts5260.c | 28 +++---
> > > > > > > drivers/misc/cardreader/rtsx_pcr.h | 17 ++++
> > > > > > > 4 files changed, 283 insertions(+), 19 deletions(-)
> > > > > > >
> > > > > > > diff --git a/drivers/misc/cardreader/rts5227.c
> > > > > > b/drivers/misc/cardreader/rts5227.c
> > > > > > > index 747391e3fb5d..8859011672cb 100644
> > > > > > > --- a/drivers/misc/cardreader/rts5227.c
> > > > > > > +++ b/drivers/misc/cardreader/rts5227.c
> > > > > > > @@ -72,15 +72,80 @@ static void
> > rts5227_fetch_vendor_settings(struct
> > > > > > rtsx_pcr *pcr)
> > > > > > >
> > > > > > > pci_read_config_dword(pdev, PCR_SETTING_REG2, &reg);
> > > > > > > pcr_dbg(pcr, "Cfg 0x%x: 0x%x\n", PCR_SETTING_REG2, reg);
> > > > > > > + if (rtsx_check_mmc_support(reg))
> > > > > > > + pcr->extra_caps |= EXTRA_CAPS_NO_MMC;
> > > > > > > pcr->sd30_drive_sel_3v3 = rtsx_reg_to_sd30_drive_sel_3v3(reg);
> > > > > > > if (rtsx_reg_check_reverse_socket(reg))
> > > > > > > pcr->flags |= PCR_REVERSE_SOCKET;
> > > > > > > }
> > > > > > >
> > > > > > > +static void rts5227_init_from_cfg(struct rtsx_pcr *pcr)
> > > > > > > +{
> > > > > > > + struct pci_dev *pdev = pcr->pci;
> > > > > > > + int l1ss;
> > > > > > > + u32 lval;
> > > > > > > + struct rtsx_cr_option *option = &pcr->option;
> > > > > > > +
> > > > > > > + l1ss = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_L1SS);
> > > > > > > + if (!l1ss)
> > > > > > > + return;
> > > > > > > +
> > > > > > > + pci_read_config_dword(pdev, l1ss + PCI_L1SS_CTL1, &lval);
> > > > > >
> > > > > > This looks a little problematic. PCI_L1SS_CTL1 is an architected
> > > > > > register in the ASPM L1 PM Substates capability, and its value may
> > > > > > change at runtime because drivers/pci/pcie/aspm.c manages it.
> > > > > >
> > > > > > It looks like the code below does device-specific configuration based
> > > > > > on the current PCI_L1SS_CTL1 value. But what happens if aspm.c
> > > > > > changes PCI_L1SS_CTL1 later?
> > > > >
> > > > > We are going to make sure and set the best configuration on the
> > > > > current time, if host change the capability later, it doesn't affect
> > > > > function, only affect a little power saving
> > > >
> > > > Why don't you unconditionally do the following?
> > > >
> > > > rtsx_set_dev_flag(pcr, ASPM_L1_1_EN);
> > > > rtsx_set_dev_flag(pcr, ASPM_L1_2_EN);
> > > > rtsx_set_dev_flag(pcr, PM_L1_1_EN);
> > > > rtsx_set_dev_flag(pcr, PM_L1_2_EN);
> > >
> > > Our power saving function have 2 different flow L1 and L1substate,
> > > so we need to check it for which flow we are going to
> > > Detail to see below reply
> > >
> > > > Let's assume the generic code in aspm.c has cleared all these bits:
> > > >
> > > > PCI_L1SS_CTL1_ASPM_L1_1
> > > > PCI_L1SS_CTL1_ASPM_L1_2
> > > > PCI_L1SS_CTL1_PCIPM_L1_1
> > > > PCI_L1SS_CTL1_PCIPM_L1_2
> > > >
> > > > in the L1 PM Substates capability.
> > > >
> > > > I think you are saying that if you *also* clear ASPM_L1_1_EN,
> > > > ASPM_L1_2_EN, PM_L1_1_EN, and PM_L1_2_EN in your device-specific
> > > > registers, it uses less power than if you set those device-specific
> > > > bits. Right?
> > > >
> > > > And moreover, I think you're saying that if aspm.c subsequently *sets*
> > > > some of those bits in the L1 PM Substates capability, those substates
> > > > *work* even though the device-specific ASPM_L1_1_EN, ASPM_L1_2_EN,
> > > > PM_L1_1_EN, and PM_L1_2_EN bits are not set. Right?
> > > >
> > > > I do not feel good about this as a general strategy. I think we
> > > > should program the device so the behavior is completely predictable,
> > > > regardless of the generic enable bits happened to be set at
> > > > probe-time.
> > > >
> > > > The current approach means that if we enable L1 substates after the
> > > > driver probe, the device is configured differently than if we enabled
> > > > L1 substates before probe. That's not a reliable way to operate it.
> > >
> > > Talk about our power saving function
> > > a) basic L1 power saving
> > > b) advance L1 power saving
> > > c) advance L1 substate power saving
> >
> > I have no idea what the difference between "basic L1 power saving" and
> > "advance L1 power saving" is, so I assume those are device-specific
> > things. If not, please use the same terminology as the PCIe spec.
> >
> > > at initial, we check pci port support L1 subs or not, if not we are
> > > going to b) otherwise going to c).
> >
> > You're not checking whether the port *supports* L1 substates. You
> > would look at PCI_L1SS_CAP to learn that. You're looking at
> > PCI_L1SS_CTL1, which tells you whether L1 substates are *enabled*.
> >
> > > Assume aspm.c change bit of L1 PM Substates capability after our
> > > driver probe, we are going to a)
> > >
> > > So far we did not see any platform change L1 PM Substates capability
> > > after our driver probe.
> >
> > You should expect that aspm.c will change bits in the L1 PM *control*
> > register (PCI_L1SS_CTL1) after probe.
> >
> > You might not actually see it change, depending on how you tested, but
> > you cannot rely on PCI_L1SS_CTL1 being constant. It may change based
> > on power/performance tradeoffs, e.g., whether the system is plugged
> > into AC power, whether it's idle, etc.
> >
>
> Our ASPM function is a HW solution follow the PCIe SPEC. don’t worry
> about crash the system If HOST change our device config space
> setting at run time our HW will do the corresponding things which
> follows the SPEC. At initial time we set these parameter just good
> for more power saving

OK. It would be better if your hardware would notice the
PCI_L1SS_CTL1 change and set its own device-specific power-saving
parameters. The drivers would be simpler, and the device behavior
would be more consistent.

Drivers *writing* to standard PCI config things (64-byte config header
or Capabilities like PCIe, PM, ASPM, L1 Substates) is a definite
problem because the PCI core owns those and writes from drivers need
to be mediated somehow. AFAICT your drivers don't write to these
things.

Drivers *reading* these things (as your drivers do) shouldn't cause
problems, but it does violate the interface abstractions that the PCI
core should provide.

Bjorn

Next message: Mathieu Desnoyers: "Re: [PATCH 1/2 v6] rseq/membarrier: add MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ"
Previous message: Marek Behún: "[PATCH leds + devicetree v2 1/2] leds: trigger: add trigger sources validating method and helper functions"
In reply to: 吳昊澄 Ricky: "RE: [PATCH v5 2/2] misc: rtsx: Add power saving functions and fix driving parameter"
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