SPI controllers accessible via spi_master driver (HSPI, VSPI) can be used to work with SD cards. The driver which provides this capability is called "SD SPI Host", due to its similarity with the SDMMC Host <sdmmc_host> driver.
In SPI mode, SD driver has lower throughput than in 1-line SD mode. However SPI mode makes pin selection more flexible, as SPI peripheral can be connected to any ESP32 pins using GPIO Matrix. SD SPI driver uses software controlled CS signal. Currently SD SPI driver assumes that it can use the SPI controller exclusively, so applications which need to share SPI bus between SD cards and other peripherals need to make sure that SD card and other devices are not used at the same time from different tasks.
SD SPI driver is represented using an :cppsdmmc_host_t structure initialized using :cSDSPI_HOST_DEFAULT macro. For slot initialization, :cSDSPI_SLOT_CONFIG_DEFAULT can be used to fill in default pin mapping, which is the same as the pin mapping in SD mode.
SD SPI driver APIs are very similar to SDMMC host APIs <sdmmc_host>. As with the SDMMC host driver, only :cppsdspi_host_init, :cppsdspi_host_init_slot, and :cppsdspi_host_deinit functions are normally used by the applications. Other functions are called by the protocol level driver via function pointers in :cppsdmmc_host_t structure.
See SD/SDIO/MMC Driver <../storage/sdmmc> for the higher level driver which implements the protocol layer.