Re: [Qemu-devel] [PATCH 4/8] Add universal DMA helper functions

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Feb 24, 2012 at 02:27:39PM +1100, David Gibson wrote:
> Not that long ago, every device implementation using DMA directly
> accessed guest memory using cpu_physical_memory_*().  This meant that
> adding support for a guest visible IOMMU would require changing every
> one of these devices to go through IOMMU translation.
> 
> Shortly before qemu 1.0, I made a start on fixing this by providing
> helper functions for PCI DMA.  These are currently just stubs which
> call the direct access functions, but mean that an IOMMU can be
> implemented in one place, rather than for every PCI device.
> 
> Clearly, this doesn't help for non PCI devices, which could also be
> IOMMU translated on some platforms.  It is also problematic for the
> devices which have both PCI and non-PCI version (e.g. OHCI, AHCI) - we
> cannot use the the pci_dma_*() functions, because they assume the
> presence of a PCIDevice, but we don't want to have to check between
> pci_dma_*() and cpu_physical_memory_*() every time we do a DMA in the
> device code.
> 
> This patch makes the first step on addressing both these problems, by
> introducing new (stub) dma helper functions which can be used for any
> DMA capable device.
> 
> These dma functions take a DMAContext *, a new (currently empty)
> variable describing the DMA address space in which the operation is to
> take place.  NULL indicates untranslated DMA directly into guest
> physical address space.  The intention is that in future non-NULL
> values will given information about any necessary IOMMU translation.
> 
> DMA using devices must obtain a DMAContext (or, potentially, contexts)
> from their bus or platform.  For now this patch just converts the PCI
> wrappers to be implemented in terms of the universal wrappers,
> converting other drivers can take place over time.
> 
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Joerg Rodel <Joerg.Rodel@amd.com>
> Cc: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
> Cc: Richard Henderson <rth@twiddle.net>
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

I'm a bit confused with all the stubbing going on.
Is this the final form of the pci_* functions or just
a stub? If the final form, we probably should just
open-code them - they don't buy us much.
If not, let's add a comment?

> ---
>  dma.h    |   87 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  hw/pci.h |   21 ++++++++------
>  2 files changed, 99 insertions(+), 9 deletions(-)
> 
> diff --git a/dma.h b/dma.h
> index 79be131..d7428df 100644
> --- a/dma.h
> +++ b/dma.h
> @@ -28,6 +28,93 @@ typedef enum {
>      DMA_DIRECTION_FROM_DEVICE = 1,
>  } DMADirection;
>  
> +typedef struct DMAContext {

why do we need the empty struct? Someone
will allocate an instance of it?
If not,
typedef struct DMAContext DMAContext;
in qemu-common.h would be enough.

> +
> +typedef void DMAInvalidateMapFunc(void *);
> +
> +static inline int dma_memory_rw(DMAContext *dma, dma_addr_t addr,
> +                                void *buf, dma_addr_t len, DMADirection dir)
> +{
> +    cpu_physical_memory_rw(addr, buf, (target_phys_addr_t)len,
> +                           dir == DMA_DIRECTION_FROM_DEVICE);
> +    return 0;
> +}
> +
> +static inline int dma_memory_read(DMAContext *dma, dma_addr_t addr,
> +                                  void *buf, dma_addr_t len)
> +{
> +    return dma_memory_rw(dma, addr, buf, len, DMA_DIRECTION_TO_DEVICE);
> +}
> +
> +static inline int dma_memory_write(DMAContext *dma, dma_addr_t addr,
> +                                   const void *buf, dma_addr_t len)
> +{
> +    return dma_memory_rw(dma, addr, (void *)buf, len,
> +                         DMA_DIRECTION_FROM_DEVICE);
> +}
> +
> +static inline void *dma_memory_map(DMAContext *dma,
> +                                   DMAInvalidateMapFunc *cb, void *opaque,
> +                                   dma_addr_t addr, dma_addr_t *len,
> +                                   DMADirection dir)
> +{
> +    target_phys_addr_t xlen = *len;
> +    void *p;
> +
> +    p = cpu_physical_memory_map(addr, &xlen,
> +                                dir == DMA_DIRECTION_FROM_DEVICE);
> +    *len = xlen;
> +    return p;
> +}
> +
> +static inline void dma_memory_unmap(DMAContext *dma,
> +                                    void *buffer, dma_addr_t len,
> +                                    DMADirection dir, dma_addr_t access_len)
> +{
> +    return cpu_physical_memory_unmap(buffer, (target_phys_addr_t)len,
> +                                     dir == DMA_DIRECTION_FROM_DEVICE,
> +                                     access_len);
> +}
> +
> +#define DEFINE_LDST_DMA(_lname, _sname, _bits, _end) \
> +    static inline uint##_bits##_t ld##_lname##_##_end##_dma(DMAContext *dma, \
> +                                                            dma_addr_t addr) \
> +    {                                                                   \
> +        uint##_bits##_t val;                                            \
> +        dma_memory_read(dma, addr, &val, (_bits) / 8);                  \
> +        return _end##_bits##_to_cpu(val);                               \
> +    }                                                                   \
> +    static inline void st##_sname##_##_end##_dma(DMAContext *dma,       \
> +                                                 dma_addr_t addr,       \
> +                                                 uint##_bits##_t val)   \
> +    {                                                                   \
> +        val = cpu_to_##_end##_bits(val);                                \
> +        dma_memory_write(dma, addr, &val, (_bits) / 8);                 \
> +    }
> +
> +static inline uint8_t ldub_dma(DMAContext *dma, dma_addr_t addr)
> +{
> +    uint8_t val;
> +
> +    dma_memory_read(dma, addr, &val, 1);
> +    return val;
> +}
> +
> +static inline void stb_dma(DMAContext *dma, dma_addr_t addr, uint8_t val)
> +{
> +    dma_memory_write(dma, addr, &val, 1);
> +}
> +
> +DEFINE_LDST_DMA(uw, w, 16, le);
> +DEFINE_LDST_DMA(l, l, 32, le);
> +DEFINE_LDST_DMA(q, q, 64, le);
> +DEFINE_LDST_DMA(uw, w, 16, be);
> +DEFINE_LDST_DMA(l, l, 32, be);
> +DEFINE_LDST_DMA(q, q, 64, be);
> +
> +#undef DEFINE_LDST_DMA
> +
>  struct ScatterGatherEntry {
>      dma_addr_t base;
>      dma_addr_t len;
> diff --git a/hw/pci.h b/hw/pci.h
> index ee53f26..64734a1 100644
> --- a/hw/pci.h
> +++ b/hw/pci.h
> @@ -544,10 +544,15 @@ static inline uint32_t pci_config_size(const PCIDevice *d)
>  }
>  
>  /* DMA access functions */
> +static inline DMAContext *pci_dma_context(PCIDevice *dev)
> +{
> +    return NULL;

This is a stub, right? Pls add a comment.

> +}
> +
>  static inline int pci_dma_rw(PCIDevice *dev, dma_addr_t addr,
>                               void *buf, dma_addr_t len, DMADirection dir)
>  {
> -    cpu_physical_memory_rw(addr, buf, len, dir == DMA_DIRECTION_FROM_DEVICE);
> +    dma_memory_rw(pci_dma_context(dev), addr, buf, len, dir);
>      return 0;
>  }
>  
> @@ -567,12 +572,12 @@ static inline int pci_dma_write(PCIDevice *dev, dma_addr_t addr,
>      static inline uint##_bits##_t ld##_l##_pci_dma(PCIDevice *dev,      \
>                                                     dma_addr_t addr)     \
>      {                                                                   \
> -        return ld##_l##_phys(addr);                                     \
> +        return ld##_l##_dma(pci_dma_context(dev), addr);                \
>      }                                                                   \
>      static inline void st##_s##_pci_dma(PCIDevice *dev,                 \
> -                          dma_addr_t addr, uint##_bits##_t val)         \
> +                                        dma_addr_t addr, uint##_bits##_t val) \
>      {                                                                   \
> -        st##_s##_phys(addr, val);                                       \
> +        st##_s##_dma(pci_dma_context(dev), addr, val);                  \
>      }
>  
>  PCI_DMA_DEFINE_LDST(ub, b, 8);
> @@ -586,21 +591,19 @@ PCI_DMA_DEFINE_LDST(q_be, q_be, 64);
>  #undef PCI_DMA_DEFINE_LDST
>  
>  static inline void *pci_dma_map(PCIDevice *dev, dma_addr_t addr,
> +                                DMAInvalidateMapFunc *cb, void *opaque,
>                                  dma_addr_t *plen, DMADirection dir)
>  {
> -    target_phys_addr_t len = *plen;
>      void *buf;
>  
> -    buf = cpu_physical_memory_map(addr, &len, dir == DMA_DIRECTION_FROM_DEVICE);
> -    *plen = len;
> +    buf = dma_memory_map(pci_dma_context(dev), cb, opaque, addr, plen, dir);
>      return buf;
>  }
>  
>  static inline void pci_dma_unmap(PCIDevice *dev, void *buffer, dma_addr_t len,
>                                   DMADirection dir, dma_addr_t access_len)
>  {
> -    cpu_physical_memory_unmap(buffer, len, dir == DMA_DIRECTION_FROM_DEVICE,
> -                              access_len);
> +    dma_memory_unmap(pci_dma_context(dev), buffer, len, dir, access_len);
>  }
>  
>  static inline void pci_dma_sglist_init(QEMUSGList *qsg, PCIDevice *dev,
> -- 
> 1.7.9