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

[Jonas Gorski]

On Mon, 20 Mar 2023 at 19:28, Álvaro Fernández Rojas <noltari@xxxxxxxxx> 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@xxxxxxxxx/
> - https://patchwork.kernel.org/project/netdevbpf/patch/20230317113427.302162-2-noltari@xxxxxxxxx/
> - https://patchwork.kernel.org/project/netdevbpf/patch/20230317113427.302162-3-noltari@xxxxxxxxx/
> - https://patchwork.kernel.org/project/netdevbpf/patch/20230317113427.302162-4-noltari@xxxxxxxxx/
> As discussed, it was an ABI break and not the correct way of fixing the issue.
>
> Signed-off-by: Álvaro Fernández Rojas <noltari@xxxxxxxxx>
> ---
>  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)
> +
> +#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)

On nitpick here: AFACT, what you are actually getting there as phy_id
isn't the phy_id but the port_id, it just happens to be identical for
internal ports.

So in theory you would first need to convert this to the appropriate
phy_id (+ which bus) first, else you risk reading from the wrong
device (and/or bus).

See how the phys_mii_mask is based on the indexes of the user ports,
not their actual phy_ids. [1] [2]

[1] https://elixir.bootlin.com/linux/latest/source/net/dsa/dsa.c#L660
[2] https://elixir.bootlin.com/linux/latest/source/include/net/dsa.h#L596

Regards
Jonas