MFC: r342634 (partial)
o Don't allocate resources for SDMA in sdhci(4) if the controller or the
front-end doesn't support SDMA or the latter implements a platform-
specific transfer method instead. While at it, factor out allocation
and freeing of SDMA resources to sdhci_dma_{alloc,free}() in order to
keep the code more readable when adding support for ADMA variants.o Base the size of the SDMA bounce buffer on MAXPHYS up to the maximum
of 512 KiB instead of using a fixed 4-KiB-buffer. With the default MAXPHYS of 128 KiB and depending on the controller and medium, this reduces the number of SDHCI interrupts by a factor of ~16 to ~32 on sequential reads while an increase of throughput of up to ~84 % was seen. Front-ends for broken controllers that only support an SDMA buffer boundary of a specific size may set SDHCI_QUIRK_BROKEN_SDMA_BOUNDARY and supply a size via struct sdhci_slot. According to Linux, only - unsupported in stable/10 anyway - Qualcomm MSM-type SDHCI controllers are affected by this, though. Requested by: Shreyank Amartya (unconditional bump to 512 KiB)
o Introduce a SDHCI_DEPEND macro for specifying the dependency of the
front-end modules on the sdhci(4) one and bump the module version of sdhci(4) to 2 via an also newly introduced SDHCI_VERSION in order to ensure that all components are in sync WRT struct sdhci_slot.
o In sdhci(4):
- Make pointers const were applicable, and
- replace a few device_printf(9) calls with slot_printf() for consistency.