linux-kernel - Re: [PATCH v4 3/3] PCI: imx6: Add code to support i.MX7D

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Date:   Thu, 16 Feb 2017 10:12:20 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Rob Herring <robh@...nel.org>
Cc:     Andrey Smirnov <andrew.smirnov@...il.com>,
        linux-pci@...r.kernel.org, yurovsky@...il.com,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Lee Jones <lee.jones@...aro.org>,
        Fabio Estevam <fabio.estevam@....com>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] PCI: imx6: Add code to support i.MX7D

Am Mittwoch, den 15.02.2017, 11:17 -0600 schrieb Rob Herring:
> On Tue, Feb 07, 2017 at 07:50:27AM -0800, Andrey Smirnov wrote:
> > Add various bits of code needed to support i.MX7D variant of the IP.
> > 
> > Cc: yurovsky@...il.com
> > Cc: Lucas Stach <l.stach@...gutronix.de>
> > Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> > Cc: Rob Herring <robh+dt@...nel.org>
> > Cc: Mark Rutland <mark.rutland@....com>
> > Cc: Lee Jones <lee.jones@...aro.org>
> > Cc: Fabio Estevam <fabio.estevam@....com>
> > Cc: linux-arm-kernel@...ts.infradead.org
> > Cc: devicetree@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> > Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
> > ---
> >  .../devicetree/bindings/pci/fsl,imx6q-pcie.txt     |  13 ++-
> >  drivers/pci/host/pci-imx6.c                        | 121 ++++++++++++++++-----
> >  include/linux/mfd/syscon/imx7-iomuxc-gpr.h         |   4 +
> >  3 files changed, 112 insertions(+), 26 deletions(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt
> > index 83aeb1f..11db2ab 100644
> > --- a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt
> > +++ b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt
> > @@ -4,7 +4,11 @@ This PCIe host controller is based on the Synopsis Designware PCIe IP
> >  and thus inherits all the common properties defined in designware-pcie.txt.
> >  
> >  Required properties:
> > -- compatible: "fsl,imx6q-pcie", "fsl,imx6sx-pcie", "fsl,imx6qp-pcie"
> > +- compatible:
> > +	- "fsl,imx6q-pcie"
> > +	- "fsl,imx6sx-pcie",
> > +	- "fsl,imx6qp-pcie"
> > +	- "fsl,imx7d-pcie"
> >  - reg: base address and length of the PCIe controller
> >  - interrupts: A list of interrupt outputs of the controller. Must contain an
> >    entry for each entry in the interrupt-names property.
> > @@ -34,6 +38,13 @@ Additional required properties for imx6sx-pcie:
> >  - clock names: Must include the following additional entries:
> >  	- "pcie_inbound_axi"
> >  
> > +Additional required properties for imx7d-pcie:
> > +- power-domains: Must be set to a phandle pointing to PCIE_PHY power domain
> 
> This domain is just the PHY? Seems like this needs a separate PHY 
> driver.
> 
No, it's called the PHY power domain, as that is probably the part that
draws the most power, but the PCIe core also looses it's state when this
domain is powered down. So it's probably the complete core that is
inside this domain.

> > +- resets: Must contain phandles to PCIE related reset lines exposed by SRC IP block
> > +- reset-names: Must contain the following entires:
> > +  	       - "pciephy"
> 
> And for this too.
> 
> > +	       - "apps"
> > +
> >  Example:
> >  
> >  	pcie@...1000000 {
> 
> [...]
> 
> > @@ -251,6 +261,10 @@ static void imx6_pcie_assert_core_reset(struct imx6_pcie *imx6_pcie)
> >  	u32 val, gpr1, gpr12;
> >  
> >  	switch (imx6_pcie->variant) {
> > +	case IMX7D:
> > +		reset_control_assert(imx6_pcie->pciephy_reset);
> > +		reset_control_assert(imx6_pcie->apps_reset);
> > +		break;
> >  	case IMX6SX:
> >  		regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR12,
> >  				   IMX6SX_GPR12_PCIE_TEST_POWERDOWN,
> 
> So the difference with i.MX7D is not really that it has a reset or not, 
> but some platforms use a reset driver and some do not. The latter should 
> be fixed.

The resets on anything before i.MX7 are not in a separate reset driver,
but are just some signals from the PCIe core wired into a syscon (IOMUX
GPR) area. While we could invent a reset controller for those, I don't
see how this would improve things. Especially as the reset on i.MX6
seems to be some side-effect of the "power-down" signal of the core, so
not strictly a reset.

Also I don't see why we should change the binding for the driver with a
long history of deployed DTs. That seems like a total waste of manpower.

Regards,
Lucas