linux-kernel - Re: [PATCH net-next v5 05/14] net: fman: Map the base address once

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Date:   Mon, 17 Oct 2022 17:15:09 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Sean Anderson <sean.anderson@...o.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        Camelia Groza <camelia.groza@....com>,
        Madalin Bucur <madalin.bucur@....com>,
        open list <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH net-next v5 05/14] net: fman: Map the base address once

Hi Sean,

On Sat, Sep 3, 2022 at 12:00 AM Sean Anderson <sean.anderson@...o.com> wrote:
> We don't need to remap the base address from the resource twice (once in
> mac_probe() and again in set_fman_mac_params()). We still need the
> resource to get the end address, but we can use a single function call
> to get both at once.
>
> While we're at it, use platform_get_mem_or_io and devm_request_resource
> to map the resource. I think this is the more "correct" way to do things
> here, since we use the pdev resource, instead of creating a new one.
> It's still a bit tricky, since we need to ensure that the resource is a
> child of the fman region when it gets requested.
>
> Signed-off-by: Sean Anderson <sean.anderson@...o.com>
> Acked-by: Camelia Groza <camelia.groza@....com>

Thanks for your patch, which is now commit 262f2b782e255b79
("net: fman: Map the base address once") in v6.1-rc1.

> --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth_sysfs.c
> +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth_sysfs.c
> @@ -18,7 +18,7 @@ static ssize_t dpaa_eth_show_addr(struct device *dev,
>
>         if (mac_dev)
>                 return sprintf(buf, "%llx",
> -                               (unsigned long long)mac_dev->res->start);
> +                               (unsigned long long)mac_dev->vaddr);

On 32-bit:

    warning: cast from pointer to integer of different size
[-Wpointer-to-int-cast]

Obviously you should cast to "uintptr_t" or "unsigned long" instead,
and change the "%llx" to "%p" or "%lx"...

However, taking a closer look:
  1. The old code exposed a physical address to user space, the new
     code exposes the mapped virtual address.
     Is that change intentional?
  2. Virtual addresses are useless in user space.
     Moreover, addresses printed by "%p" are obfuscated, as this is
     considered a security issue. Likewise for working around this by
     casting to an integer.

What's the real purpose of dpaa_eth_show_addr()?
Perhaps it should be removed?

>         else
>                 return sprintf(buf, "none");
>  }

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds