Hi,
I'm trying to understand the SATA/AHCI protocol and the libata library in linux.
The SATA/AHCI protocol has many operation modes to chose from,
like Command based or FIS based, DMA yes/no, specifiying FIFO depth,
SATA mode or ATAPI/IDE mode, and there is also something with SCSI etc. etc.
Does there exist a (linux) tool which can give information about the current
configuration of the SATA/AHCI host controller?
Another question is: when the sata/ahci driver gets loaded, to which degree
is libata involved in the device initialisation process (for example assigning
FIS base address, assigning FIFO buffers etc.)?
I stumbled upon this problem because a driver says in its P0FB (offset 0x0108)
port register, that it uses the address 0x4a060400 (ARM 32bit platform) as its
FIS base address.
The spec says the normal FIS receive area size is 256 bytes.
But then it says that when using FIS-based switching, software shall allocate
a FIS receive area that is 16 times larger than the normal FIS receive area
size, ie. 4096 bytes.
I couldn't determine yet whether the normal FIS receive area is in use
or a different 4096-byte memory area.
In the normal case the address is required to be 256-byte aligned,
and in the other case 4096-byte aligned.
But neither of these requirements holds for the above address.
So, I suspect the device is not optimally configured. And also the device
performance is very slow.
OTOH I couldn't find any indication in the driver code that it sets this FIS
address,
so then is it a device issue (default reset-values?), or could it perhaps be a
libata issue?
# cat /proc/iomem
01c18000-01c18fff : sata@1c18000
...
40000000-7fffffff : System RAM
40008000-40afffff : Kernel code
40c00000-40cb59cf : Kernel data
Thx
--
U.Mutlu
