linux-kernel - 答复: 答复: [PATCH v6] mfd: Add support for RTS5250S power saving

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Message-ID: <2A308283684ECD4B896628E09AF5361E01A8193C@RS-MBS01.realsil.com.cn>
Date:   Tue, 19 Dec 2017 08:15:24 +0000
From:   冯锐 <rui_feng@...lsil.com.cn>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     "lee.jones@...aro.org" <lee.jones@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: 答复: 答复: [PATCH v6] mfd: Add support for RTS5250S power saving

> On Fri, Dec 15, 2017 at 09:42:45AM +0000, 冯锐 wrote:
> > > [+cc Hans, Dave, linux-pci]
> > >
> > > On Thu, Sep 07, 2017 at 04:26:39PM +0800, rui_feng@...lsil.com.cn
> wrote:
> > > > From: Rui Feng <rui_feng@...lsil.com.cn>
> > >
> > > I wish this had been posted to linux-pci before being merged.
> > >
> > > I'm concerned because some of this appears to overlap and conflict
> > > with PCI core management of ASPM.
> > >
> > > I assume these devices advertise ASPM support in their Link
> > > Capabilites registers, right?  If so, why isn't the existing PCI
> > > core ASPM support sufficient?
> > >
> > When L1SS is configured, the device(hardware) can't enter L1SS status
> > automatically, it need driver(software) to do some work to achieve the
> function.
> 
> So this is a hardware defect in the device?  As far as I know, ASPM and L1SS
> are specified such that they should work without special driver support.
> 
Yes, you can say that.

> > > > Enable power saving for RTS5250S as following steps:
> > > > 1.Set 0xFE58 to enable clock power management.
> > >
> > > Is this clock power management something specific to RTS5250S, or is
> > > it standard PCIe architected stuff?
> > >
> > 0xFE58 is specific register to RTS5250S not standard PCIe architected stuff.
> 
> OK.  I asked because devices often mirror architected PCIe config things in
> device-specific MMIO space, and if I squint just right, I can sort of match up the
> register bits you used with things in the PCIe spec.
> 
> > > > 2.Check cfg space whether support L1SS or not.
> > >
> > > This sounds like standard PCIe ASPM L1 Substates, right?
> > >
> > Yes.
> >
> > > > 3.If support L1SS, set 0xFF03 to free clkreq.
> > > > 4.When entering idle status, enable aspm
> > > >   and set parameters for L1SS and LTR.
> > > > 5.Wnen entering run status, disable aspm
> > > >   and set parameters for L1SS and LTR.
> > >
> > > In general, drivers should not configure ASPM, L1SS, and LTR
> > > themselves; the PCI core should do that.
> > >
> > > If a driver needs to tweak ASPM at run-time, it should use
> > > interfaces exported by the PCI core to do so.
> > >
> > Which interface I can use to set ASPM? I use "pci_write_config_byte" now.
> 
> What do you need to do?  include/linux/pci-aspm.h exports
> pci_disable_link_state(), which is mainly used to avoid ASPM states that have
> hardware errata.
> 
I want to enable ASPM(L0 -> L1) and disable ASPM(L1 -> L0), which interface can I use?

> If you need to do something beyond that, we can talk about adding something
> new.
> 
> There are quite a few other things in include/linux/pci-aspm.h, but they're all
> for internal use in the PCI core.  I'll move them to drivers/pci/pci.h to avoid
> confusion.
> 
> > > > +static void rts5249_set_aspm(struct rtsx_pcr *pcr, bool enable) {
> > > > +	struct rtsx_cr_option *option = &pcr->option;
> > > > +	u8 val = 0;
> > > > +
> > > > +	if (pcr->aspm_enabled == enable)
> > > > +		return;
> > > > +
> > > > +	if (option->dev_aspm_mode == DEV_ASPM_DYNAMIC) {
> > > > +		if (enable)
> > > > +			val = pcr->aspm_en;
> > > > +		rtsx_pci_update_cfg_byte(pcr,
> > > > +			pcr->pcie_cap + PCI_EXP_LNKCTL,
> > > > +			ASPM_MASK_NEG, val);
> > >
> > > This stomps on whatever ASPM configuration the PCI core did.
> > We disable/enable aspm dynamic in order to improve read/write
> > performance and more stable, so we don't allow PCI core do it.
> 
> This is pretty vague.  Can you be any more specific?  If there are
> performance or stability problems in the PCI core ASPM support, I'd prefer to
> fix those instead of working around them in every driver.
> 
It's device's defect not PCI core, so no need to fix PCI core.

> Bjorn
> 
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