netdev - Re: [PATCH 10/12] net: fec: use dma_alloc_noncoherent for data cache enabled coldfire

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Date: Tue, 17 Oct 2023 10:43:19 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Christoph Hellwig <hch@....de>
Cc: Greg Ungerer <gerg@...ux-m68k.org>, iommu@...ts.linux.dev, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Conor Dooley <conor@...nel.org>, Geert Uytterhoeven <geert+renesas@...der.be>, 
	Magnus Damm <magnus.damm@...il.com>, Robin Murphy <robin.murphy@....com>, 
	Marek Szyprowski <m.szyprowski@...sung.com>, Wei Fang <wei.fang@....com>, 
	Shenwei Wang <shenwei.wang@....com>, Clark Wang <xiaoning.wang@....com>, 
	NXP Linux Team <linux-imx@....com>, linux-m68k@...ts.linux-m68k.org, netdev@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, linux-renesas-soc@...r.kernel.org, 
	Jim Quinlan <james.quinlan@...adcom.com>
Subject: Re: [PATCH 10/12] net: fec: use dma_alloc_noncoherent for data cache
 enabled coldfire

Hi Christoph,

On Mon, Oct 16, 2023 at 7:48 AM Christoph Hellwig <hch@....de> wrote:
> Coldfire platforms with data caches can't properly implement
> dma_alloc_coherent and currently just return noncoherent memory from
> dma_alloc_coherent.
>
> The fec driver than works around this with a flush of all caches in the
> receive path. Make this hack a little less bad by using the explicit
> dma_alloc_noncoherent API and documenting the hacky cache flushes so
> that the DMA API level hack can be removed.
>
> Also replace the check for CONFIG_M532x for said hack with a check
> for COLDFIRE && !COLDFIRE_COHERENT_DMA.  While m532x is the only such
> platform with a fec module, this makes the code more consistent and
> easier to follow.
>
> Signed-off-by: Christoph Hellwig <hch@....de>

Thanks for your patch!

> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -406,6 +406,70 @@ static void fec_dump(struct net_device *ndev)
>         } while (bdp != txq->bd.base);
>  }
>
> +/*
> + * Coldfire does not support DMA coherent allocations, and has historically used
> + * a band-aid with a manual flush in fec_enet_rx_queue.
> + */
> +#if defined(CONFIG_COLDFIRE) && !defined(CONFIG_COLDFIRE_COHERENT_DMA)
> +static void *fec_dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
> +               gfp_t gfp)
> +{
> +       return dma_alloc_noncoherent(dev, size, handle, DMA_BIDIRECTIONAL, gfp);
> +}
> +
> +static void fec_dma_free(struct device *dev, size_t size, void *cpu_addr,
> +               dma_addr_t handle)
> +{
> +       dma_free_noncoherent(dev, size, cpu_addr, handle, DMA_BIDIRECTIONAL);
> +}
> +#else /* CONFIG_COLDFIRE && !CONFIG_COLDFIRE_COHERENT_DMA */

!CONFIG_COLDFIRE || CONFIG_COLDFIRE_COHERENT_DMA

> +static void *fec_dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
> +               gfp_t gfp)
> +{
> +       return dma_alloc_coherent(dev, size, handle, gfp);
> +}
> +
> +static void fec_dma_free(struct device *dev, size_t size, void *cpu_addr,
> +               dma_addr_t handle)
> +{
> +       dma_free_coherent(dev, size, cpu_addr, handle);
> +}
> +#endif /* !CONFIG_COLDFIRE && !CONFIG_COLDFIRE_COHERENT_DMA */

!CONFIG_COLDFIRE || CONFIG_COLDFIRE_COHERENT_DMA

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