netdev - Re: [RFC PATCH] drivers: net: dsa: b53: mmap: add phy ops

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Date:   Mon, 20 Mar 2023 20:58:32 +0100
From:   Álvaro Fernández Rojas <noltari@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     jonas.gorski@...il.com, andrew@...n.ch, olteanv@...il.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] drivers: net: dsa: b53: mmap: add phy ops

El lun, 20 mar 2023 a las 20:06, Florian Fainelli
(<f.fainelli@...il.com>) escribió:
>
> On 3/20/23 11:28, Álvaro Fernández Rojas wrote:
> > Currently, B53 MMAP BCM63xx devices with an external switch hang when
> > performing PHY read and write operations due to invalid registers access.
> > This adds support for PHY ops by using the internal bus from mdio-mux-bcm6368
> > when probed by device tree and also falls back to direct MDIO registers if not.
> >
> > This is an alternative to:
> > - https://patchwork.kernel.org/project/netdevbpf/cover/20230317113427.302162-1-noltari@gmail.com/
> > - https://patchwork.kernel.org/project/netdevbpf/patch/20230317113427.302162-2-noltari@gmail.com/
> > - https://patchwork.kernel.org/project/netdevbpf/patch/20230317113427.302162-3-noltari@gmail.com/
> > - https://patchwork.kernel.org/project/netdevbpf/patch/20230317113427.302162-4-noltari@gmail.com/
> > As discussed, it was an ABI break and not the correct way of fixing the issue.
>
> Looks good for the most part, just a few questions below.
>
> >
> > Signed-off-by: Álvaro Fernández Rojas <noltari@...il.com>
> > ---
> >   drivers/net/dsa/b53/b53_mmap.c    | 86 +++++++++++++++++++++++++++++++
> >   include/linux/platform_data/b53.h |  1 +
> >   2 files changed, 87 insertions(+)
> >
> > diff --git a/drivers/net/dsa/b53/b53_mmap.c b/drivers/net/dsa/b53/b53_mmap.c
> > index 706df04b6cee..7deca1c557c5 100644
> > --- a/drivers/net/dsa/b53/b53_mmap.c
> > +++ b/drivers/net/dsa/b53/b53_mmap.c
> > @@ -19,14 +19,25 @@
> >   #include <linux/bits.h>
> >   #include <linux/kernel.h>
> >   #include <linux/module.h>
> > +#include <linux/of_mdio.h>
> >   #include <linux/io.h>
> >   #include <linux/platform_device.h>
> >   #include <linux/platform_data/b53.h>
> >
> >   #include "b53_priv.h"
> >
> > +#define REG_MDIOC            0xb0
> > +#define  REG_MDIOC_EXT_MASK  BIT(16)
> > +#define  REG_MDIOC_REG_SHIFT 20
> > +#define  REG_MDIOC_PHYID_SHIFT       25
> > +#define  REG_MDIOC_RD_MASK   BIT(30)
> > +#define  REG_MDIOC_WR_MASK   BIT(31)
>
> For some reason, there was no bit introduced to tell us when a
> transaction has finished, so we have to poll after a certain delay has
> elapsed...

Yeah... :(

>
> > +
> > +#define REG_MDIOD            0xb4
> > +
> >   struct b53_mmap_priv {
> >       void __iomem *regs;
> > +     struct mii_bus *bus;
> >   };
> >
> >   static int b53_mmap_read8(struct b53_device *dev, u8 page, u8 reg, u8 *val)
> > @@ -216,6 +227,69 @@ static int b53_mmap_write64(struct b53_device *dev, u8 page, u8 reg,
> >       return 0;
> >   }
> >
> > +static inline void b53_mmap_mdio_read(struct b53_device *dev, int phy_id,
> > +                                   int loc, u16 *val)
> > +{
> > +     uint32_t reg;
> > +
> > +     b53_mmap_write32(dev, 0, REG_MDIOC, 0);
> > +
> > +     reg = REG_MDIOC_RD_MASK |
> > +           (phy_id << REG_MDIOC_PHYID_SHIFT) |
> > +           (loc << REG_MDIOC_REG_SHIFT);
> > +
> > +     b53_mmap_write32(dev, 0, REG_MDIOC, reg);
> > +     udelay(50);
> > +     b53_mmap_read16(dev, 0, REG_MDIOD, val);
> > +}
> > +
> > +static inline int b53_mmap_mdio_write(struct b53_device *dev, int phy_id,
> > +                                   int loc, u16 val)
> > +{
> > +     uint32_t reg;
> > +
> > +     b53_mmap_write32(dev, 0, REG_MDIOC, 0);
> > +
> > +     reg = REG_MDIOC_WR_MASK |
> > +           (phy_id << REG_MDIOC_PHYID_SHIFT) |
> > +           (loc << REG_MDIOC_REG_SHIFT) |
> > +           val;
> > +
> > +     b53_mmap_write32(dev, 0, REG_MDIOC, reg);
> > +     udelay(50);
> > +
> > +     return 0;
> > +}
> > +
> > +static int b53_mmap_phy_read16(struct b53_device *dev, int addr, int reg,
> > +                            u16 *value)
> > +{
> > +     struct b53_mmap_priv *priv = dev->priv;
> > +     struct mii_bus *bus = priv->bus;
> > +
> > +     if (bus)
> > +             *value = mdiobus_read_nested(bus, addr, reg);
>
> Since you make the 'mii-bus' property and 'priv->bus' necessary
> prerequisites for the driver to finish probing successfully, when shall
> we not have valid priv->bus reference to work with? Do we end-up taking
> the other path at all?

Yes, but only if the driver is probed from platform data and not from
device tree.

> --
> Florian
>

--
Álvaro.