Re: [PATCH v2 1/2] EmbeddedPkg/NonCoherentDmaLib: implement support for DMA range limits

["Ard Biesheuvel" <ard.biesheuvel@linaro.org>]

On Tue, 26 Nov 2019 at 13:04, Leif Lindholm <leif.lindholm@linaro.org> wrote:
>
> On Tue, Nov 26, 2019 at 00:12:41 +0100, Ard Biesheuvel wrote:
> > Implement support for driving peripherals with limited DMA ranges to
> > NonCoherentDmaLib, by adding a device address limit, and taking it,
> > along with the device offset, into account when allocating or mapping
> > DMA buffers.
> >
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > ---
> >  EmbeddedPkg/EmbeddedPkg.dec                                 |   6 +
> >  EmbeddedPkg/Library/NonCoherentDmaLib/NonCoherentDmaLib.c   | 165 ++++++++++++++++++--
> >  EmbeddedPkg/Library/NonCoherentDmaLib/NonCoherentDmaLib.inf |   1 +
> >  3 files changed, 160 insertions(+), 12 deletions(-)
> >
> > diff --git a/EmbeddedPkg/EmbeddedPkg.dec b/EmbeddedPkg/EmbeddedPkg.dec
> > index 8812a6db7c30..69922802f473 100644
> > --- a/EmbeddedPkg/EmbeddedPkg.dec
> > +++ b/EmbeddedPkg/EmbeddedPkg.dec
> > @@ -186,6 +186,12 @@ [PcdsFixedAtBuild.common, PcdsDynamic.common]
> >    #
> >    gEmbeddedTokenSpaceGuid.PcdDmaDeviceOffset|0x0|UINT64|0x0000058
> >
> > +  #
> > +  # Highest address value supported by the device for DMA addressing. Note
> > +  # that this value should be strictly greater than PcdDmaDeviceOffset.
> > +  #
> > +  gEmbeddedTokenSpaceGuid.PcdDmaDeviceLimit|0xFFFFFFFFFFFFFFFF|UINT64|0x000005A
> > +
> >    #
> >    # Selection between DT and ACPI as a default
> >    #
> > diff --git a/EmbeddedPkg/Library/NonCoherentDmaLib/NonCoherentDmaLib.c b/EmbeddedPkg/Library/NonCoherentDmaLib/NonCoherentDmaLib.c
> > index 78220f6358aa..115345765435 100644
> > --- a/EmbeddedPkg/Library/NonCoherentDmaLib/NonCoherentDmaLib.c
> > +++ b/EmbeddedPkg/Library/NonCoherentDmaLib/NonCoherentDmaLib.c
> > @@ -40,6 +40,8 @@ typedef struct {
> >  STATIC EFI_CPU_ARCH_PROTOCOL      *mCpu;
> >  STATIC LIST_ENTRY                 UncachedAllocationList;
> >
> > +STATIC PHYSICAL_ADDRESS           mDmaHostAddressLimit;
> > +
> >  STATIC
> >  PHYSICAL_ADDRESS
> >  HostToDeviceAddress (
> > @@ -49,6 +51,102 @@ HostToDeviceAddress (
> >    return (PHYSICAL_ADDRESS)(UINTN)Address + PcdGet64 (PcdDmaDeviceOffset);
> >  }
> >
> > +/**
> > +  Allocates one or more 4KB pages of a certain memory type at a specified
> > +  alignment.
> > +
> > +  Allocates the number of 4KB pages specified by Pages of a certain memory type
> > +  with an alignment specified by Alignment. The allocated buffer is returned.
> > +  If Pages is 0, then NULL is returned. If there is not enough memory at the
> > +  specified alignment remaining to satisfy the request, then NULL is returned.
> > +  If Alignment is not a power of two and Alignment is not zero, then ASSERT().
> > +  If Pages plus EFI_SIZE_TO_PAGES (Alignment) overflows, then ASSERT().
> > +
> > +  @param  MemoryType            The type of memory to allocate.
> > +  @param  Pages                 The number of 4 KB pages to allocate.
> > +  @param  Alignment             The requested alignment of the allocation.
> > +                                Must be a power of two.
> > +                                If Alignment is zero, then byte alignment is
> > +                                used.
> > +
> > +  @return A pointer to the allocated buffer or NULL if allocation fails.
> > +
> > +**/
> > +STATIC
> > +VOID *
> > +InternalAllocateAlignedPages (
> > +  IN EFI_MEMORY_TYPE  MemoryType,
> > +  IN UINTN            Pages,
> > +  IN UINTN            Alignment
> > +  )
> > +{
> > +  EFI_STATUS            Status;
> > +  EFI_PHYSICAL_ADDRESS  Memory;
> > +  UINTN                 AlignedMemory;
> > +  UINTN                 AlignmentMask;
> > +  UINTN                 UnalignedPages;
> > +  UINTN                 RealPages;
> > +
> > +  //
> > +  // Alignment must be a power of two or zero.
> > +  //
> > +  ASSERT ((Alignment & (Alignment - 1)) == 0);
>
> Sorry, slight mental glitch (and I realise this is in  copied code) -
> the above also matches for an Alignment of 1, which contradicts the
> comment. Clearly requesting allocation explicitly aligned to 1 is a)
> silly, b) the same as what happens for any value <= EFI_PAGE_SIZE
> in the below code, and c) harmless, but could you update the comment?
>
> If so:
> Acked-by: Leif Lindholm <leif.lindholm@linaro.org>
>

Given that 1 == 2^0, it is also a power of 2, and so the comment is
accurate imho