Re: Scatter-gather list constraints

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To: David Vrabel <david.vrabel@...>
Cc: Kernel development list <linux-kernel@...>, AntonioLin <antonio.lin@...>, <linux-usb@...>, Perez-Gonzalez, Inaky <inaky.perez-gonzalez@...>
Date: Monday, June 23, 2008 - 3:45 pm

On Mon, 23 Jun 2008, David Vrabel wrote:


Yes, there are two fields in struct request_queue for this: 
max_phys_segments (the driver's limit) and max_hw_segments (the 
hardware's limit).

Standard EHCI hardware requires that the memory locations of the data
for each packet be "virtually contiguous", i.e., discontiguities are
allowed only at 4-KB page boundaries.  This severely limits the ability
to handle general S-G lists.  For example, a 1024-byte packet can't be
broken up into two 512-byte pieces unless the first piece ends at a
page boundary and the second piece begins at a page boundary.  Maybe
HWA host controllers are required to be more flexible, I don't know.

This may mean that your suggested approach won't work.

Alan Stern

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Messages in current thread:
Scatter-gather list constraints, Alan Stern, (Fri Jun 20, 4:30 pm)
Re: Scatter-gather list constraints, David Vrabel, (Mon Jun 23, 10:46 am)
Re: Scatter-gather list constraints, Alan Stern, (Mon Jun 23, 11:12 am)
Re: Scatter-gather list constraints, David Vrabel, (Mon Jun 23, 3:06 pm)
RE: Scatter-gather list constraints, Perez-Gonzalez, Inaky, (Wed Jun 25, 12:02 am)
RE: Scatter-gather list constraints, Alan Stern, (Wed Jun 25, 10:24 am)
RE: Scatter-gather list constraints, Perez-Gonzalez, Inaky, (Thu Jun 26, 12:43 pm)
RE: Scatter-gather list constraints, Alan Stern, (Thu Jun 26, 3:34 pm)
Re: Scatter-gather list constraints, Inaky Perez-Gonzalez, (Thu Jun 26, 6:39 pm)
Re: Scatter-gather list constraints, Alan Stern, (Mon Jun 23, 3:45 pm)
Re: Scatter-gather list constraints, Stefan Richter, (Mon Jun 23, 5:53 pm)
Re: Scatter-gather list constraints, Andi Kleen, (Sat Jun 21, 9:59 am)
Re: Scatter-gather list constraints, Alan Stern, (Sat Jun 21, 10:54 am)
Re: Scatter-gather list constraints, Andi Kleen, (Sat Jun 21, 11:21 am)
Re: Scatter-gather list constraints, Alan Stern, (Sat Jun 21, 5:50 pm)
Re: Scatter-gather list constraints, FUJITA Tomonori, (Tue Jun 24, 6:41 am)
Re: Scatter-gather list constraints, Alan Stern, (Tue Jun 24, 10:57 am)
Re: Scatter-gather list constraints, FUJITA Tomonori, (Tue Jun 24, 8:18 pm)
Re: Scatter-gather list constraints, Alan Stern, (Wed Jun 25, 10:23 am)
Re: Scatter-gather list constraints, FUJITA Tomonori, (Wed Jun 25, 10:06 pm)
Re: Scatter-gather list constraints, FUJITA Tomonori, (Thu Jun 26, 1:39 am)
Re: Scatter-gather list constraints, Jens Axboe, (Thu Jun 26, 2:35 am)
Re: Scatter-gather list constraints, Alan Stern, (Thu Jun 26, 10:18 am)
Re: Scatter-gather list constraints, FUJITA Tomonori, (Thu Jun 26, 2:58 am)
Re: Scatter-gather list constraints, Jens Axboe, (Thu Jun 26, 8:39 am)
Re: Scatter-gather list constraints, Boaz Harrosh, (Thu Jun 26, 11:16 am)
Re: Scatter-gather list constraints, Jens Axboe, (Thu Jun 26, 1:39 pm)
Re: Scatter-gather list constraints, Alan Stern, (Thu Jun 26, 11:12 am)
Re: Scatter-gather list constraints, Jens Axboe, (Thu Jun 26, 1:41 pm)
Re: Scatter-gather list constraints, Alan Stern, (Wed Aug 27, 5:32 pm)
Re: Scatter-gather list constraints, Andi Kleen, (Thu Jun 26, 8:54 am)
Re: Scatter-gather list constraints, Jens Axboe, (Thu Jun 26, 9:00 am)
Re: Scatter-gather list constraints, Andi Kleen, (Sat Jun 21, 7:00 pm)
Re: Scatter-gather list constraints, Alan Stern, (Sun Jun 22, 10:35 am)
Re: Scatter-gather list constraints, David Miller, (Fri Jun 20, 4:50 pm)