Re: [edk2-devel] [PATCH v4 edk2-platforms 1/1] Silicon/DesignWare/Driver: DwEmacSnpDxe: Add DesignWare EMAC driver

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

On Wed, 19 Jun 2019 at 12:09, Ooi, Tzy Way <tzy.way.ooi@intel.com> wrote:
>
> Hi Bieshuevel,
>
> In the DmaMap function, there is one line where my code look like this:
>
> "Status = DmaMap (MapOperationBusMasterCommonBuffer, Snp->MacDriver.TxdescRing[0], &BufferSize, &Snp->MacDriver.TxdescRingMap[0], &Snp->MappingTxdesc);"
>
> You asked me why the [0] and how many descriptor I am mapping. In my code, there is total 10 descriptors. The way I did in current code was I use DmaAllocateBuffer to allocate a memory size which is big enough for 10 descriptors. After that, I just map the first descriptor and I access the rest of the descriptor by using the first descriptor address plus the size for each descriptor to get the next descriptor address. Wonder if this method is ok? Or do I need to use DmaAllocateBuffer and DmaMap for 10 times for total 10 descriptors?
>

No, this is not ok. You have to allocate and map the size of the
memory that you will use. As long as you don't use more than a page,
it will not matter in practice, but it is wrong nonetheless