linux-kernel - Re: [RFC PATCH v3 3/7] iommu/arm-smmu-v3: support ops registration for CDX bus

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Message-ID: <CAGETcx_W8QVe+CdpocN2rHjp08TwsW22FaJgrYW=0JNge_N6KQ@mail.gmail.com>
Date:   Tue, 6 Sep 2022 17:10:34 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Nipun Gupta <nipun.gupta@....com>
Cc:     robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        gregkh@...uxfoundation.org, rafael@...nel.org,
        eric.auger@...hat.com, alex.williamson@...hat.com,
        cohuck@...hat.com, puneet.gupta@....com,
        song.bao.hua@...ilicon.com, mchehab+huawei@...nel.org,
        maz@...nel.org, f.fainelli@...il.com, jeffrey.l.hugo@...il.com,
        Michael.Srba@...nam.cz, mani@...nel.org, yishaih@...dia.com,
        jgg@...pe.ca, jgg@...dia.com, robin.murphy@....com,
        will@...nel.org, joro@...tes.org, masahiroy@...nel.org,
        ndesaulniers@...gle.com, linux-arm-kernel@...ts.infradead.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, kvm@...r.kernel.org, okaya@...nel.org,
        harpreet.anand@....com, nikhil.agarwal@....com,
        michal.simek@....com, aleksandar.radovanovic@....com, git@....com
Subject: Re: [RFC PATCH v3 3/7] iommu/arm-smmu-v3: support ops registration
 for CDX bus

On Tue, Sep 6, 2022 at 6:48 AM Nipun Gupta <nipun.gupta@....com> wrote:
>
> With new CDX bus supported for AMD FPGA devices on ARM
> platform, the bus requires registration for the SMMU v3
> driver.
>
> Signed-off-by: Nipun Gupta <nipun.gupta@....com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index d32b02336411..8ec9f2baf12d 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -29,6 +29,7 @@
>  #include <linux/platform_device.h>
>
>  #include <linux/amba/bus.h>
> +#include <linux/cdx/cdx_bus.h>
>
>  #include "arm-smmu-v3.h"
>  #include "../../iommu-sva-lib.h"
> @@ -3690,16 +3691,27 @@ static int arm_smmu_set_bus_ops(struct iommu_ops *ops)
>                 if (err)
>                         goto err_reset_pci_ops;
>         }
> +#endif
> +#ifdef CONFIG_CDX_BUS
> +       if (cdx_bus_type.iommu_ops != ops) {
> +               err = bus_set_iommu(&cdx_bus_type, ops);
> +               if (err)
> +                       goto err_reset_amba_ops;
> +       }

I'm not an expert on IOMMUs, so apologies if the question is stupid.

Why does the CDX bus need special treatment here (like PCI) when there
are so many other busses (eg: I2C, SPI, etc) that don't need any
changes here?

-Saravana

>  #endif
>         if (platform_bus_type.iommu_ops != ops) {
>                 err = bus_set_iommu(&platform_bus_type, ops);
>                 if (err)
> -                       goto err_reset_amba_ops;
> +                       goto err_reset_cdx_ops;
>         }
>
>         return 0;
>
> -err_reset_amba_ops:
> +err_reset_cdx_ops:
> +#ifdef CONFIG_CDX_BUS
> +       bus_set_iommu(&cdx_bus_type, NULL);
> +#endif
> +err_reset_amba_ops: __maybe_unused;
>  #ifdef CONFIG_ARM_AMBA
>         bus_set_iommu(&amba_bustype, NULL);
>  #endif
> --
> 2.25.1
>