Re: [rfc/patch] libata -- port configurable delays
From: Jeff Garzik
Date: Fri May 13 2005 - 18:25:57 EST
Alan Cox wrote:
On Gwe, 2005-05-13 at 19:58, Benjamin LaHaise wrote:
is available at http://www.kvack.org/~bcrl/simple-aio-min_nr.c).
Before this patch __delay() is the number one entry in oprofile
results for this workload. Does this look like a reasonable approach
for chipsets that aren't completely braindead? Cheers,
If your chipset implements the 400nS lockout in hardware it certainly
seems to make sense. Nice to know someone has put it in hardware
No, it's just mostly irrelevant under SATA.
Under SATA you are -not- talking to a device when you touch
Status/AltStatus, you are talking to the host controller. Specifically,
you're talking to a controller buffer that stores a copy of the ATA
shadow registers.
The ATA registers are transmitted to the device in a single packet,
called a FIS, when the Command or Device Control register is written.
When the device updates its status, or completes a command, it sends a
FIS from device to controller, instructing the controller to update its
cached copy of the Status register.
You're bitbanging a buffer, in SATA.
Jeff
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