Re: [PATCH] net: fec: set dma_coherent_mask

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Greg Ungerer <gerg@linux-m68k.org>
Cc: netdev <netdev@vger.kernel.org>, Linux/m68k <linux-m68k@vger.kernel.org>
Subject: Re: [PATCH] net: fec: set dma_coherent_mask
Date: Tue, 27 Mar 2018 14:59:23 +0200	[thread overview]
Message-ID: <CAMuHMdW_ZmN9aptLoSK7JYLVaLyErkFyGU2sb2f564uCUeBh6w@mail.gmail.com> (raw)
In-Reply-To: <1522071386-29743-1-git-send-email-gerg@linux-m68k.org>

Hi Greg,

On Mon, Mar 26, 2018 at 3:36 PM, Greg Ungerer <gerg@linux-m68k.org> wrote:
> As of commit 205e1b7f51e4 ("dma-mapping: warn when there is no
> coherent_dma_mask") the Freescale FEC driver is issuing the following
> warning on driver initialization on ColdFire systems:
>
> WARNING: CPU: 0 PID: 1 at ./include/linux/dma-mapping.h:516 0x40159e20
> Modules linked in:
> CPU: 0 PID: 1 Comm: swapper Not tainted 4.16.0-rc7-dirty #4
> Stack from 41833dd8:
>         41833dd8 40259c53 40025534 40279e26 00000003 00000000 4004e514 41827000
>         400255de 40244e42 00000204 40159e20 00000009 00000000 00000000 4024531d
>         40159e20 40244e42 00000204 00000000 00000000 00000000 00000007 00000000
>         00000000 40279e26 4028d040 40226576 4003ae88 40279e26 418273f6 41833ef8
>         7fffffff 418273f2 41867028 4003c9a2 4180ac6c 00000004 41833f8c 4013e71c
>         40279e1c 40279e26 40226c16 4013ced2 40279e26 40279e58 4028d040 00000000
> Call Trace:
>         [<40025534>] 0x40025534
>  [<4004e514>] 0x4004e514
>  [<400255de>] 0x400255de
>  [<40159e20>] 0x40159e20
>  [<40159e20>] 0x40159e20
>
> It is not fatal, the driver and the system continue to function normally.
>
> As per the warning the coherent_dma_mask is not set on this device.
> There is nothing special about the DMA memory coherency on this hardware
> so we can just set the mask to 32bits during probe.
>
> Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>

Thanks for your patch!

> ---
>  drivers/net/ethernet/freescale/fec_main.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> Is this the best way to handle this problem?
> Comments welcome...
>
> diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
> index d4604bc..3cb130a 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -2702,6 +2702,8 @@ static int fec_enet_alloc_queue(struct net_device *ndev)
>         int ret = 0;
>         struct fec_enet_priv_tx_q *txq;
>
> +       dma_set_coherent_mask(&fep->pdev->dev, DMA_BIT_MASK(32));
> +
>         for (i = 0; i < fep->num_tx_queues; i++) {
>                 txq = kzalloc(sizeof(*txq), GFP_KERNEL);
>                 if (!txq) {

As per your other email, this does not trigger on iMX systems using DT.
Hence I'm wondering if the Coldfire platform code shouldn't just do the
same what drivers/of/device.c does, cfr.
https://www.spinics.net/lists/linux-m68k/msg10929.html?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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