linux-kernel - Re: [PATCH] New config added to handle 64-bit systems with 32-bit DMA support

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Date: Wed, 19 Jun 2024 13:43:31 +0200
From: Michael Nazzareno Trimarchi <michael@...rulasolutions.com>
To: Robin Murphy <robin.murphy@....com>
Cc: Alberto Secondi <albertosecondi@...il.com>, hch@....de, m.szyprowski@...sung.com, 
	iommu@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	alberto.secondi@...nsula.com, Davide Salaris <davide.salaris@...nsula.com>
Subject: Re: [PATCH] New config added to handle 64-bit systems with 32-bit DMA support

Hi Robin

On Wed, Jun 19, 2024 at 12:36 PM Robin Murphy <robin.murphy@....com> wrote:
>
> On 2024-06-19 10:17 am, Alberto Secondi wrote:
> > ------ Tessian Warning ------
> >
> > Be careful, the email's sending address "albertosecondi@...il[.]com" has never been seen on your company's network before today
> >
> > This warning message will be removed if you reply to or forward this email to a recipient outside of your organization.
> >
> > ---- Tessian Warning End ----
> >
> > From: Alberto Secondi <alberto.secondi@...nsula.com>
> >
> > The kernel assumes that 64-bit systems have 64-bit DMA support through
> > CONFIG_ARCH_DMA_ADDR_T_64BIT. This is not always true; for example, several
> > iMX8 systems (verified on iMX8MM and iMX8MP) have DMA with only 32-bit support.
> > This results in several drivers requesting DMA_BIT_MASK(64), which causes
> > malfunctions, particularly when systems have more than 3GB of DRAM (verified
> > with the lan743x driver and iMX8 systems with 4GB of DRAM). Therefore, a new
> > config ARCH_64BIT_HAS_DMA32_ONLY was added to manage 64-bit systems with 32-bit
> > DMA, which adjusts DMA_BIT_MASK(n) accordingly.
>
> No. If a system has devices naturally capable of >32-bit DMA, and memory
> at >32-bit system physical addresses, but only a 32-bit interconnect in
> between, that needs to be described properly in Devicetree/ACPI, not
> hacked around with completely non-portable kernel bodges.
>

commit 4251a3ac4de9625a284a9c046cc915487e9b2a5e
Author: Lucas Stach <l.stach@...gutronix.de>
Date:   Tue May 4 10:20:51 2021 +0200

    arm64: dts: imx8mm: specify dma-ranges

    DMA addressing capabilities on i.MX8MM are limited by the interconnect,
    same as on i.MX8MQ. Add dma-ranges to the the peripheral bus to let
    the kernel know about this.

    Signed-off-by: Lucas Stach <l.stach@...gutronix.de>
    Reviewed-by: Frieder Schrempf <frieder.schrempf@...tron.de>
    Tested-by: Frieder Schrempf <frieder.schrempf@...tron.de>
    Signed-off-by: Shawn Guo <shawnguo@...nel.org>

diff --git a/arch/arm64/boot/dts/freescale/imx8mm.dtsi
b/arch/arm64/boot/dts/freescale/imx8mm.dtsi
index 64aa38fd2b6e0..e7648c3b83905 100644
--- a/arch/arm64/boot/dts/freescale/imx8mm.dtsi
+++ b/arch/arm64/boot/dts/freescale/imx8mm.dtsi
@@ -261,6 +261,7 @@ soc@0 {
                #address-cells = <1>;
                #size-cells = <1>;
                ranges = <0x0 0x0 0x0 0x3e000000>;
+               dma-ranges = <0x40000000 0x0 0x40000000 0xc0000000>;
                nvmem-cells = <&imx8mm_uid>;
                nvmem-cell-names = "soc_unique_id";


Somenthing like this should already do it?

Michael

> Thanks,
> Robin.
>
> > Signed-off-by: Alberto Secondi <alberto.secondi@...nsula.com>
> > Co-developed-by: Davide Salaris <davide.salaris@...nsula.com>
> > ---
> >   include/linux/dma-mapping.h | 4 ++++
> >   kernel/dma/Kconfig          | 8 ++++++++
> >   2 files changed, 12 insertions(+)
> >
> > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> > index f693aafe221f..629220a777e3 100644
> > --- a/include/linux/dma-mapping.h
> > +++ b/include/linux/dma-mapping.h
> > @@ -74,7 +74,11 @@
> >    */
> >   #define DMA_MAPPING_ERROR           (~(dma_addr_t)0)
> >
> > +#ifdef CONFIG_ARCH_64BIT_HAS_DMA32_ONLY
> > +#define DMA_BIT_MASK(n)      (((n) > 32) ? ((1ULL<<(32))-1) : ((1ULL<<(n))-1))
> > +#else
> >   #define DMA_BIT_MASK(n)     (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
> > +#endif
> >
> >   #ifdef CONFIG_DMA_API_DEBUG
> >   void debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr);
> > diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> > index c06e56be0ca1..0a27eafed808 100644
> > --- a/kernel/dma/Kconfig
> > +++ b/kernel/dma/Kconfig
> > @@ -36,6 +36,14 @@ config NEED_DMA_MAP_STATE
> >   config ARCH_DMA_ADDR_T_64BIT
> >       def_bool 64BIT || PHYS_ADDR_T_64BIT
> >
> > +config ARCH_64BIT_HAS_DMA32_ONLY
> > +        bool "64bit System has DMA32 only"
> > +        depends on ARCH_DMA_ADDR_T_64BIT
> > +        default n
> > +     help
> > +       This enables forcing the maximum DMA_BIT_MASK to 32 bits for
> > +       64-bit systems that have DMA support limited to 32 bits.
> > +
> >   config ARCH_HAS_DMA_SET_MASK
> >       bool
> >
>