Re: [PATCH] MdeModulePkg/SdMmcPciHcDxe: Use 16/32-bit IO widths

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

On Fri, 1 Feb 2019 at 06:55, Wu, Hao A <hao.a.wu@intel.com> wrote:
>
> > -----Original Message-----
> > From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Jeff
> > Brasen
> > Sent: Thursday, January 31, 2019 7:59 AM
> > To: edk2-devel@lists.01.org
> > Cc: Edgar Handal; Jeff Brasen
> > Subject: [edk2] [PATCH] MdeModulePkg/SdMmcPciHcDxe: Use 16/32-bit IO
> > widths
> >
> > From: Edgar Handal <ehandal@nvidia.com>
> >
> > Use 16-bit and 32-bit IO widths for SDMMC MMIO to prevent all register
> > accesses from being split up into 8-bit accesses.
> >
> > The SDHCI specification states that the registers shall be accessable in
> > byte, word, and double word accesses.
>

Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

I think we should always prefer accessing MMIO registers using their
native size, unless there are pressing reasons not to.


> Hi,
>
> Thanks for the contribution. The change seems good to me.
>
> Just curious, if the accesses are always slit into byte(8-bit), is there any
> issue or performance impact is encountered during your usage?
>
> It will be helpful to get more information on the purpose of the patch.
> Thanks.
>
> Best Regards,
> Hao Wu
>
> >
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Jeff Brasen <jbrasen@nvidia.com>
> > ---
> >  MdeModulePkg/Bus/Pci/SdMmcPciHcDxe/SdMmcPciHci.c | 25
> > ++++++++++++++++++++----
> >  1 file changed, 21 insertions(+), 4 deletions(-)
> >
> > diff --git a/MdeModulePkg/Bus/Pci/SdMmcPciHcDxe/SdMmcPciHci.c
> > b/MdeModulePkg/Bus/Pci/SdMmcPciHcDxe/SdMmcPciHci.c
> > index 5aec8c6..82f4493 100644
> > --- a/MdeModulePkg/Bus/Pci/SdMmcPciHcDxe/SdMmcPciHci.c
> > +++ b/MdeModulePkg/Bus/Pci/SdMmcPciHcDxe/SdMmcPciHci.c
> > @@ -152,19 +152,36 @@ SdMmcHcRwMmio (
> >    )
> >  {
> >    EFI_STATUS                   Status;
> > +  EFI_PCI_IO_PROTOCOL_WIDTH    Width;
> >
> >    if ((PciIo == NULL) || (Data == NULL))  {
> >      return EFI_INVALID_PARAMETER;
> >    }
> >
> > -  if ((Count != 1) && (Count != 2) && (Count != 4) && (Count != 8)) {
> > -    return EFI_INVALID_PARAMETER;
> > +  switch (Count) {
> > +    case 1:
> > +      Width = EfiPciIoWidthUint8;
> > +      break;
> > +    case 2:
> > +      Width = EfiPciIoWidthUint16;
> > +      Count = 1;
> > +      break;
> > +    case 4:
> > +      Width = EfiPciIoWidthUint32;
> > +      Count = 1;
> > +      break;
> > +    case 8:
> > +      Width = EfiPciIoWidthUint32;
> > +      Count = 2;
> > +      break;
> > +    default:
> > +      return EFI_INVALID_PARAMETER;
> >    }
> >
> >    if (Read) {
> >      Status = PciIo->Mem.Read (
> >                            PciIo,
> > -                          EfiPciIoWidthUint8,
> > +                          Width,
> >                            BarIndex,
> >                            (UINT64) Offset,
> >                            Count,
> > @@ -173,7 +190,7 @@ SdMmcHcRwMmio (
> >    } else {
> >      Status = PciIo->Mem.Write (
> >                            PciIo,
> > -                          EfiPciIoWidthUint8,
> > +                          Width,
> >                            BarIndex,
> >                            (UINT64) Offset,
> >                            Count,
> > --
> > 2.7.4
> >
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