* Why no SG support for isoc
@ 2021-12-07 22:24 Thinh Nguyen
2021-12-08 2:52 ` Alan Stern
0 siblings, 1 reply; 3+ messages in thread
From: Thinh Nguyen @ 2021-12-07 22:24 UTC (permalink / raw)
To: linux-usb@vger.kernel.org; +Cc: Hans de Goede, Alan Stern, Greg Kroah-Hartman
Hi,
I came across this change fe2072cc1768 ("usb/hcd: Ensure scatter-gather
is not used for isoc transfers") and wonder why it was made. The
description doesn't explain much. I was trying to look for the archived
conversation about this but couldn't find it.
Can someone help explain why we enforce this to all hosts? Or help point
to the archived conversation with the full explanation?
Thanks,
Thinh
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: Why no SG support for isoc
2021-12-07 22:24 Why no SG support for isoc Thinh Nguyen
@ 2021-12-08 2:52 ` Alan Stern
2021-12-08 3:32 ` Thinh Nguyen
0 siblings, 1 reply; 3+ messages in thread
From: Alan Stern @ 2021-12-08 2:52 UTC (permalink / raw)
To: Thinh Nguyen; +Cc: linux-usb@vger.kernel.org, Hans de Goede, Greg Kroah-Hartman
On Tue, Dec 07, 2021 at 10:24:41PM +0000, Thinh Nguyen wrote:
> Hi,
>
> I came across this change fe2072cc1768 ("usb/hcd: Ensure scatter-gather
> is not used for isoc transfers") and wonder why it was made. The
> description doesn't explain much. I was trying to look for the archived
> conversation about this but couldn't find it.
>
> Can someone help explain why we enforce this to all hosts? Or help point
> to the archived conversation with the full explanation?
I don't remember the details; it was nine years ago. However, you can find the
email thread for the original patch submission here:
https://marc.info/?t=134122051600006&r=1&w=2
The discussion leading up to it apparently started here:
https://marc.info/?l=linux-usb&m=134098509628768&w=2
Alan Stern
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: Why no SG support for isoc
2021-12-08 2:52 ` Alan Stern
@ 2021-12-08 3:32 ` Thinh Nguyen
0 siblings, 0 replies; 3+ messages in thread
From: Thinh Nguyen @ 2021-12-08 3:32 UTC (permalink / raw)
To: Alan Stern, Thinh Nguyen
Cc: linux-usb@vger.kernel.org, Hans de Goede, Greg Kroah-Hartman
Alan Stern wrote:
> On Tue, Dec 07, 2021 at 10:24:41PM +0000, Thinh Nguyen wrote:
>> Hi,
>>
>> I came across this change fe2072cc1768 ("usb/hcd: Ensure scatter-gather
>> is not used for isoc transfers") and wonder why it was made. The
>> description doesn't explain much. I was trying to look for the archived
>> conversation about this but couldn't find it.
>>
>> Can someone help explain why we enforce this to all hosts? Or help point
>> to the archived conversation with the full explanation?
>
> I don't remember the details; it was nine years ago. However, you can find the
> email thread for the original patch submission here:
>
> https://urldefense.com/v3/__https://marc.info/?t=134122051600006&r=1&w=2__;!!A4F2R9G_pg!PaOHS9ywSls44XOUn4ZEdd9ttJtTOJnrY_kKkQNf6EtVOzQsJ5lQ7PFq4Buz1PmjSgVz$
>
> The discussion leading up to it apparently started here:
>
> https://urldefense.com/v3/__https://marc.info/?l=linux-usb&m=134098509628768&w=2__;!!A4F2R9G_pg!PaOHS9ywSls44XOUn4ZEdd9ttJtTOJnrY_kKkQNf6EtVOzQsJ5lQ7PFq4Buz1BxOj5YU$
>
> Alan Stern
>
Ok. From the discussion above and looking at the code, the main reasons
are because ehci and xhci drivers don't support SG for isoc and no class
driver in the kernel needs to use SG for isoc.
Thanks for the links Alan.
Thinh
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-12-07 22:24 Why no SG support for isoc Thinh Nguyen
2021-12-08 2:52 ` Alan Stern
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