Re: [PATCH v12 2/6] PCI: mediatek: Add new method to get shared pcie-cfg base address

[Rob Herring <robh+dt@kernel.org>]

On Tue, Aug 31, 2021 at 10:47 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Tue, Aug 31, 2021 at 10:04:40AM -0500, Rob Herring wrote:
> > On Fri, Aug 27, 2021 at 11:46 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > >
> > > On Mon, Aug 23, 2021 at 11:27:56AM +0800, Chuanjia Liu wrote:
> > > > For the new dts format, add a new method to get
> > > > shared pcie-cfg base address and use it to configure
> > > > the PCIECFG controller
> > >
> > > Rewrap this to fill 75 columns.
> > >
> > > > Signed-off-by: Chuanjia Liu <chuanjia.liu@mediatek.com>
> > > > Acked-by: Ryder Lee <ryder.lee@mediatek.com>
> > > > ---
> > > >  drivers/pci/controller/pcie-mediatek.c | 17 +++++++++++++++++
> > > >  1 file changed, 17 insertions(+)
> > > >
> > > > diff --git a/drivers/pci/controller/pcie-mediatek.c b/drivers/pci/controller/pcie-mediatek.c
> > > > index 25bee693834f..4296d9e04240 100644
> > > > --- a/drivers/pci/controller/pcie-mediatek.c
> > > > +++ b/drivers/pci/controller/pcie-mediatek.c
> > > > @@ -14,6 +14,7 @@
> > > >  #include <linux/irqchip/chained_irq.h>
> > > >  #include <linux/irqdomain.h>
> > > >  #include <linux/kernel.h>
> > > > +#include <linux/mfd/syscon.h>
> > > >  #include <linux/msi.h>
> > > >  #include <linux/module.h>
> > > >  #include <linux/of_address.h>
> > > > @@ -23,6 +24,7 @@
> > > >  #include <linux/phy/phy.h>
> > > >  #include <linux/platform_device.h>
> > > >  #include <linux/pm_runtime.h>
> > > > +#include <linux/regmap.h>
> > > >  #include <linux/reset.h>
> > > >
> > > >  #include "../pci.h"
> > > > @@ -207,6 +209,7 @@ struct mtk_pcie_port {
> > > >   * struct mtk_pcie - PCIe host information
> > > >   * @dev: pointer to PCIe device
> > > >   * @base: IO mapped register base
> > > > + * @cfg: IO mapped register map for PCIe config
> > > >   * @free_ck: free-run reference clock
> > > >   * @mem: non-prefetchable memory resource
> > > >   * @ports: pointer to PCIe port information
> > > > @@ -215,6 +218,7 @@ struct mtk_pcie_port {
> > > >  struct mtk_pcie {
> > > >       struct device *dev;
> > > >       void __iomem *base;
> > > > +     struct regmap *cfg;
> > > >       struct clk *free_ck;
> > > >
> > > >       struct list_head ports;
> > > > @@ -682,6 +686,10 @@ static int mtk_pcie_startup_port_v2(struct mtk_pcie_port *port)
> > > >               val |= PCIE_CSR_LTSSM_EN(port->slot) |
> > > >                      PCIE_CSR_ASPM_L1_EN(port->slot);
> > > >               writel(val, pcie->base + PCIE_SYS_CFG_V2);
> > > > +     } else if (pcie->cfg) {
> > > > +             val = PCIE_CSR_LTSSM_EN(port->slot) |
> > > > +                   PCIE_CSR_ASPM_L1_EN(port->slot);
> > > > +             regmap_update_bits(pcie->cfg, PCIE_SYS_CFG_V2, val, val);
> > > >       }
> > > >
> > > >       /* Assert all reset signals */
> > > > @@ -985,6 +993,7 @@ static int mtk_pcie_subsys_powerup(struct mtk_pcie *pcie)
> > > >       struct device *dev = pcie->dev;
> > > >       struct platform_device *pdev = to_platform_device(dev);
> > > >       struct resource *regs;
> > > > +     struct device_node *cfg_node;
> > > >       int err;
> > > >
> > > >       /* get shared registers, which are optional */
> > > > @@ -995,6 +1004,14 @@ static int mtk_pcie_subsys_powerup(struct mtk_pcie *pcie)
> > > >                       return PTR_ERR(pcie->base);
> > > >       }
> > > >
> > > > +     cfg_node = of_find_compatible_node(NULL, NULL,
> > > > +                                        "mediatek,generic-pciecfg");
> > >
> > > This looks wrong to me.  IIUC, since we start at NULL, this searches
> > > the entire device tree for any node with
> > >
> > >   compatible = "mediatek,generic-pciecfg"
> > >
> > > but we should only care about the specific device/node this driver
> > > claimed.
> > >
> > > Should this be part of the match data, i.e., struct mtk_pcie_soc?
> >
> > What would you put in match data exactly?
> >
> > The other way to do this is to have a DT property with the phandle
> > which people like to do (have everything in the node 'for their
> > driver'). If there's only 1 possible node (which is almost always the
> > case), then there is little benefit to having another property. It's
> > just redundant data. A phandle lookup might be a bit faster with the
> > caching we do, but on a miss it would still walk all nodes.
> >
> > The other thing with these 'extra register bits to twiddle' is that
> > they tend to be SoC specific and change from chip to chip, so either
> > way is not very portable. The real question to ask is should there be
> > a standard interface used or created.
> >
> > > > +     if (cfg_node) {
> > > > +             pcie->cfg = syscon_node_to_regmap(cfg_node);
> > >
> > > Other drivers in drivers/pci/controller/ use
> > > syscon_regmap_lookup_by_phandle() (j721e, dra7xx, keystone,
> > > layerscape, artpec6) or syscon_regmap_lookup_by_compatible() (imx6,
> > > kirin, v3-semi).
> >
> > There's no phandle to use in this case. As above, I'm trying to break
> > people of this habit.
>
> Thanks!  I was mistaken in lots of ways here.  I first assumed
> "mediatek,generic-pciecfg" was local to the pcie node, but that's not
> true.  Then I thought there might be an ownership issue because the
> regmap is not local to the device, and several drivers look up and use
> the same regmap.  But it looks like regmap provides some internal
> locking which mitigates most or all of that concern.
>
> Just to check -- you prefer syscon_regmap_lookup_by_compatible() over
> syscon_regmap_lookup_by_phandle()?

Yes, unless there is either more than 1 instance of the syscon or some
additional data specific to the user (e.g. a register offset).

Rob