Hi,
I have a (soft-IP, FPGA based, single-port) very simple SATA device
(https://github.com/enjoy-digital/litesata) that provides me (r/w)
access to a single physical SATA hard drive. I can access one sector
at a time from bare-metal C code, using DMA and the following three
MMIO register sets:
- phy:
u8 enable; // write 1 to bit 0 to enable phy
// bits 1..7 reserved
u8 status_ro ; // bit 0 = 1 if overall phy ready
// bit 1 = 1 if phy tx ready
// bit 2 = 1 if phy rx ready
// bit 3 = 1 if phy ctrl ready
- dma_writer: // write one 512-bit sector to disk
u64 sector; // 48-bit disk sector number
u64 base; // 64-bit dma base address (source buffer)
u8 start; // write 1 to bit 0 to start DMA transfer
u8 done_ro; // read 1 from bit 0 when transfer complete
u8 error_ro; // read 1 from bit 0 if transfer failed
- dma_reader: // read one 512-bit sector from disk
u64 sector; // 48-bit disk sector number
u64 base; // 64-bit dma base address (dest. buffer)
u8 start; // write 1 to bit 0 to start DMA transfer
u8 done_ro; // read 1 from bit 0 when transfer complete
u8 error_ro; // read 1 from bit 0 if transfer failed
For practice, I'm trying to write a low level SATA driver to access
the hard drive from Linux using this device.
I've tried studying existing drivers under `drivers/ata/*` to get an
idea how to "connect" my device into the Linux SATA subsystem, and
also tried studying the "libATA Developer’s Guide" at
https://www.kernel.org/doc/html/v5.18-rc5/driver-api/libata.html
It turns out there's a sizable "impedance mismatch" between my
understanding of my device's simple register interface and most of
the "production" devices for which existing drivers have been
written in `drivers/ata/*`...
I'm not even sure if I should be looking at `drivers/ata/ahci_*.c` or
rather `drivers/ata/sata_*.c` :)
I'd like some help finding an existing driver that's "closest"
conceptually to the behavior of my device (outlined above), that I can
use as a source of inspiration and as a starting point in learning about
the linux SATA subsystem.
Alternatively, is there some "guided tour to the Linux SATA subsystem"
that's a bit less of a firehose than the "LibATA Developer's Guide"?
Many thanks for any clues or pointers,
--Gabriel
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