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SubjectRe: [PATCH 4/7 v5] iommu: arm-smmu: Add support for the fsl-mc bus
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On 20/05/18 14:49, Nipun Gupta wrote:
> Implement bus specific support for the fsl-mc bus including
> registering arm_smmu_ops and bus specific device add operations.
>
> Signed-off-by: Nipun Gupta <nipun.gupta@nxp.com>
> ---
> drivers/iommu/arm-smmu.c | 7 +++++++
> drivers/iommu/iommu.c | 21 +++++++++++++++++++++
> include/linux/fsl/mc.h | 8 ++++++++
> include/linux/iommu.h | 2 ++
> 4 files changed, 38 insertions(+)
>
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 69e7c60..e1d5090 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -52,6 +52,7 @@
> #include <linux/spinlock.h>
>
> #include <linux/amba/bus.h>
> +#include <linux/fsl/mc.h>
>
> #include "io-pgtable.h"
> #include "arm-smmu-regs.h"
> @@ -1459,6 +1460,8 @@ static struct iommu_group *arm_smmu_device_group(struct device *dev)
>
> if (dev_is_pci(dev))
> group = pci_device_group(dev);
> + else if (dev_is_fsl_mc(dev))
> + group = fsl_mc_device_group(dev);
> else
> group = generic_device_group(dev);
>
> @@ -2037,6 +2040,10 @@ static void arm_smmu_bus_init(void)
> bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
> }
> #endif
> +#ifdef CONFIG_FSL_MC_BUS
> + if (!iommu_present(&fsl_mc_bus_type))
> + bus_set_iommu(&fsl_mc_bus_type, &arm_smmu_ops);
> +#endif
> }
>
> static int arm_smmu_device_probe(struct platform_device *pdev)
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index d2aa2320..6d4ce35 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -32,6 +32,7 @@
> #include <linux/pci.h>
> #include <linux/bitops.h>
> #include <linux/property.h>
> +#include <linux/fsl/mc.h>
> #include <trace/events/iommu.h>
>
> static struct kset *iommu_group_kset;
> @@ -987,6 +988,26 @@ struct iommu_group *pci_device_group(struct device *dev)
> return iommu_group_alloc();
> }
>
> +/* Get the IOMMU group for device on fsl-mc bus */
> +struct iommu_group *fsl_mc_device_group(struct device *dev)
> +{
> + struct device *cont_dev = fsl_mc_cont_dev(dev);
> + struct iommu_group *group;
> +
> + /* Container device is responsible for creating the iommu group */
> + if (fsl_mc_is_cont_dev(dev)) {

Why duplicate what fsl_mc_cont_dev() has already figured out?

AFAICS the overall operation here boils down to something like:

cont_dev = fsl_mc_cont_dev(dev);
group = iommu_group_get(cont_dev);
if (!group)
group = iommu_group_alloc();
return group;

> + group = iommu_group_alloc();
> + if (IS_ERR(group))
> + return NULL;

iommu_group_get_for_dev() expects a PTR_ERR, so I don't think munging
the return here is the right thing to do.

> + } else {
> + get_device(cont_dev);

If races are a concern, isn't this a bit late? Maybe in that case you
want {get,put}_fsl_mc_cont_dev() routines instead of the simple macro
below. But on the other hand if dev already has cont_dev as its parent,
wouldn't the reference taken in device_add() be sufficient to prevent it
from vanishing unexpectedly in this timescale?

Robin.

> + group = iommu_group_get(cont_dev);
> + put_device(cont_dev);
> + }
> +
> + return group;
> +}
> +
> /**
> * iommu_group_get_for_dev - Find or create the IOMMU group for a device
> * @dev: target device
> diff --git a/include/linux/fsl/mc.h b/include/linux/fsl/mc.h
> index f27cb14..dddaca1 100644
> --- a/include/linux/fsl/mc.h
> +++ b/include/linux/fsl/mc.h
> @@ -351,6 +351,14 @@ struct fsl_mc_io {
> #define dev_is_fsl_mc(_dev) (0)
> #endif
>
> +/* Macro to check if a device is a container device */
> +#define fsl_mc_is_cont_dev(_dev) (to_fsl_mc_device(_dev)->flags & \
> + FSL_MC_IS_DPRC)
> +
> +/* Macro to get the container device of a MC device */
> +#define fsl_mc_cont_dev(_dev) (fsl_mc_is_cont_dev(_dev) ? \
> + (_dev) : (_dev)->parent)
> +
> /*
> * module_fsl_mc_driver() - Helper macro for drivers that don't do
> * anything special in module init/exit. This eliminates a lot of
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 19938ee..2981200 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -389,6 +389,8 @@ static inline size_t iommu_map_sg(struct iommu_domain *domain,
> extern struct iommu_group *pci_device_group(struct device *dev);
> /* Generic device grouping function */
> extern struct iommu_group *generic_device_group(struct device *dev);
> +/* FSL-MC device grouping function */
> +struct iommu_group *fsl_mc_device_group(struct device *dev);
>
> /**
> * struct iommu_fwspec - per-device IOMMU instance data
>

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