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
