linux-kernel - Re: [PATCH] iommu: ipmmu-vmsa: Add DMA controllers to devices

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Message-ID: <CAMuHMdVtR_8OZG2XrD5PHY+ybaH4dudya4VXNXD3iHktdDyF8w@mail.gmail.com>
Date: Wed, 29 Oct 2025 17:08:07 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Koichiro Den <den@...inux.co.jp>
Cc: iommu@...ts.linux.dev, linux-renesas-soc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, joro@...tes.org, will@...nel.org, 
	robin.murphy@....com
Subject: Re: [PATCH] iommu: ipmmu-vmsa: Add DMA controllers to devices_allowlist

Hi Den-san,

On Mon, 27 Oct 2025 at 02:26, Koichiro Den <den@...inux.co.jp> wrote:
> Add Renesas DMA controller devices to the devices_allowlist to enable
> their use with the IPMMU. This allows DMA channels to operate through
> the IOMMU when enabled.
>
> Signed-off-by: Koichiro Den <den@...inux.co.jp>

Thanks for your patch!

> --- a/drivers/iommu/ipmmu-vmsa.c
> +++ b/drivers/iommu/ipmmu-vmsa.c
> @@ -741,7 +741,9 @@ static const char * const devices_allowlist[] = {
>         "ee100000.mmc",
>         "ee120000.mmc",
>         "ee140000.mmc",
> -       "ee160000.mmc"
> +       "ee160000.mmc",
> +       "e7350000.dma-controller",
> +       "e7351000.dma-controller"

While your change looks correct to me, it causes DMA mapping failures on
Gray Hawk Single and Sparrow Hawk when IPMMU support is enabled
(on renesas-drivers-2025-10-28-v6.18-rc3 with renesas_defconfig
+ CONFIG_IPMMU_VMSA=y):

    rcar-dmac e7351000.dma-controller: chan1: failed to map 1@...0000000e656000c
    sh-sci e6560000.serial: Failed preparing Tx DMA descriptor

0xe656000c = HSCIF2 Transmit FIFO data register.

With "#define DEBUG" added to drivers/dma/sh/rcar-dmac.c:

    rcar-dmac e7351000.dma-controller: chan1: failed to map 1@...0000000e656000c
    sh-sci e6560000.serial: Failed preparing Tx DMA descriptor
    rcar-dmac e7351000.dma-controller: chan2: map 1@...0000000e6560014
to 0x00000000fff82014 dir: DMA_TO_DEVICE
    rcar-dmac e7351000.dma-controller: chan2: chunk
00000000e5110c20/000000005e0ede90 sgl 0@...000000d8c5440, 256/256
0x00000000fff82014 -> 0x00000000ffed6000
    rcar-dmac e7351000.dma-controller: chan2: submit #2@...000005e0ede90
    rcar-dmac e7351000.dma-controller: chan2: chunk
0000000025f2f66c/00000000e5f0dd15 sgl 0@...0000064f1067f, 256/256
0x00000000fff82014 -> 0x00000000ffed6100
    rcar-dmac e7351000.dma-controller: chan2: submit #3@...00000e5f0dd15
    rcar-dmac e7351000.dma-controller: chan2: queue chunk
00000000e5110c20: 256@...0000000fff82014 -> 0x00000000ffed6000

0xe6560014 = HSCIF2 Receive FIFO data register

Comparing to the CONFIG_IPMMU_VMSA=n case:

    rcar-dmac e7351000.dma-controller: chan1: map 1@...0000000e656000c
to 0x00000000e656000c dir: DMA_FROM_DEVICE
    rcar-dmac e7351000.dma-controller: chan1: chunk
0000000096396eb4/00000000f35357b6 sgl 0@...0000013546bf6, 74/74
0x0000000489ab5000 -> 0x00000000e656000c
    rcar-dmac e7351000.dma-controller: chan1: submit #2@...00000f35357b6
    rcar-dmac e7351000.dma-controller: chan1: queue chunk
0000000096396eb4: 74@...000000489ab5000 -> 0x00000000e656000c

This confuses me even more: why no DMA_TO_DEVICE mapping in the
latter case?

>  };
>
>  static bool ipmmu_device_is_allowed(struct device *dev)

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