On Sun, May 8, 2022 at 12:34 AM Gabriel L. Somlo <gsomlo@xxxxxxxxx> wrote: > > Hi, > Hello Gabriel, > 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. > I think, first of all look at how the drivers on SATA hardware are coded under Linux kernel at low level (you are expected to know a little about Linux C standards). https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/ata/ and if it were me, I would start with ata_generic.c first: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/ata/ata_generic.c For another example, you can take a look at Bootlin source code: https://elixir.bootlin.com/linux/latest/source/drivers/ata/sata_mv.c For a working logic, take a look at this document: https://github.com/digi-embedded/linux/blob/v4.1/dey-2.2/maint/Documentation/devicetree/bindings/ata/ahci-platform.txt Right after these, you should have an idea about "Block Drivers" because you will need to contact kernel. Here is a great guide for you: http://www.embeddedlinux.org.cn/essentiallinuxdevicedrivers/final/ch14.html I think all these will be enough for you at first. Salut, Ozgur > 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 > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies@xxxxxxxxxxxxxxxxx > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
