Re: [edk2-devel] [PATCH V5 1/1] EmbeddedPkg: DwMmcHcDxe: Add support for Designware SDMMC driver

["Ard Biesheuvel" <ardb@kernel.org>]

On Tue, 27 Apr 2021 at 21:31, Kinney, Michael D
<michael.d.kinney@intel.com> wrote:
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> This is an example of another approach.  This module uses PCI I/O or IoLib based on the type of device.
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> https://github.com/tianocore/edk2/tree/master/MdeModulePkg/Bus/Pci/PciSioSerialDxe
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> No additional protocols or lib classes/instances.  Instead, the register access APIs are included in the module and based on the type of device detected, it uses PCI I/O or IoLib:
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> https://github.com/tianocore/edk2/blob/5b90b8abb4049e2d98040f548ad23b6ab22d5d19/MdeModulePkg/Bus/Pci/PciSioSerialDxe/SerialIo.c#L1327
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> https://github.com/tianocore/edk2/blob/5b90b8abb4049e2d98040f548ad23b6ab22d5d19/MdeModulePkg/Bus/Pci/PciSioSerialDxe/SerialIo.c#L1358
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> This technique could for PCI I/O vs MMIO register access.  You would need to add more APIs for the use of PCI I/O or DmaLib for DMA access.
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Is it really worth the effort to rewrite this code?

This patch has been circulating for a while now, and I fail to see the
point of refactoring and splitting up this code, given how unlikely it
is that DesignWare will ever put a real PCI frontend on this IP. The
SD/MMC override protocol was intended for implementations that are
almost SDHCI compliant, but have some quirks that need to be worked
around.