Re: [PATCH] EmbeddedPkg/DwEmmcDxe: limit max clock for platform

[Leif Lindholm <leif.lindholm@linaro.org>]

On Mon, Jul 03, 2017 at 12:01:56PM +0800, Jun Nie wrote:
> Some boards may have max clock limitation. Add a Pcd to notify
> driver.
> 
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Jun Nie <jun.nie@linaro.org>
> ---
>  EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.c   | 4 ++++
>  EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.inf | 1 +
>  EmbeddedPkg/EmbeddedPkg.dec                 | 1 +
>  3 files changed, 6 insertions(+)
> 
> diff --git a/EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.c b/EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.c
> index fe23d11..308f3a7 100644
> --- a/EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.c
> +++ b/EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.c
> @@ -560,6 +560,10 @@ DwEmmcSetIos (
>    EFI_STATUS Status = EFI_SUCCESS;
>    UINT32    Data;
>  
> +  if (BusClockFreq > PcdGet32 (PcdDwEmmcDxeMaxClockFrequencyInHz)) {

This snippet means that any platform that was using this driver
successfully, but where BusClockFreq is higher than the default value
of this Pcd will stop working.

> +    return EFI_UNSUPPORTED;
> +  }
> +
>    if (TimingMode != EMMCBACKWARD) {
>      Data = MmioRead32 (DWEMMC_UHSREG);
>      switch (TimingMode) {
> diff --git a/EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.inf b/EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.inf
> index e3c8313..3582997 100644
> --- a/EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.inf
> +++ b/EmbeddedPkg/Drivers/DwEmmcDxe/DwEmmcDxe.inf
> @@ -48,6 +48,7 @@
>  [Pcd]
>    gEmbeddedTokenSpaceGuid.PcdDwEmmcDxeBaseAddress
>    gEmbeddedTokenSpaceGuid.PcdDwEmmcDxeClockFrequencyInHz
> +  gDwEmmcDxeTokenSpaceGuid.PcdDwEmmcDxeMaxClockFrequencyInHz
>  
>  [Depex]
>    TRUE
> diff --git a/EmbeddedPkg/EmbeddedPkg.dec b/EmbeddedPkg/EmbeddedPkg.dec
> index 0d4a062..aec8259 100644
> --- a/EmbeddedPkg/EmbeddedPkg.dec
> +++ b/EmbeddedPkg/EmbeddedPkg.dec
> @@ -167,6 +167,7 @@
>    # DwEmmc Driver PCDs
>    gEmbeddedTokenSpaceGuid.PcdDwEmmcDxeBaseAddress|0x0|UINT32|0x00000035
>    gEmbeddedTokenSpaceGuid.PcdDwEmmcDxeClockFrequencyInHz|0x0|UINT32|0x00000036
> +  gDwEmmcDxeTokenSpaceGuid.PcdDwEmmcDxeMaxClockFrequencyInHz|0x0|UINT32|400000000

And this definition sets the default value of this Pcd to 0. Meaning
that all existing drivers would stop working.
Also, 0x00000037 would seem like a more suitable Token than 400000000.

If introducing a new limit value like this, I would strongly recommend
making "0" a magic value meaning "no restrictions".

i.e.
  UINT32 MaxFreq;
  MaxFreq = PcdGet32 (PcdDwEmmcDxeMaxClockFrequencyInHz);
  if ((MaxFreq != 0) && (BusClockFreq > MaxFreq)) {

/
    Leif

>  
>    #
>    # Android FastBoot
> -- 
> 1.9.1
>