Re: [RFC PATCH] usb: xhci-mtk: handle bandwidth table rollover

HI,

On Wed, Aug 11, 2021 at 5:02 PM Chunfeng Yun (云春峰)
[off-list ref] wrote:

On Mon, 2021-08-09 at 17:42 +0800, Ikjoon Jang wrote:

quoted

On Mon, Aug 9, 2021 at 5:11 PM Greg Kroah-Hartman
[off-list ref] wrote:

quoted

On Mon, Aug 09, 2021 at 04:59:29PM +0800, Ikjoon Jang wrote:

quoted

xhci-mtk has 64 slots for periodic bandwidth calculations and
each
slot represents byte budgets on a microframe. When an endpoint's
allocation sits on the boundary of the table, byte budgets' slot
should be rolled over but the current implementation doesn't.

This patch applies a 6 bits mask to the microframe index to
handle
its rollover 64 slots and prevent out-of-bounds array access.

Signed-off-by: Ikjoon Jang <redacted>
---

 drivers/usb/host/xhci-mtk-sch.c | 79 +++++++++----------------
--------
 drivers/usb/host/xhci-mtk.h     |  1 +
 2 files changed, 23 insertions(+), 57 deletions(-)

Why is this "RFC"?  What needs to be addressed in this change
before it
can be accepted?

sorry, I had to mention why this is RFC:

I simply don't know about the details of the xhci-mtk internals.
It was okay from my tests with mt8173 and I think this will be
harmless
as this is "better than before".

But when I removed get_esit_boundary(), I really have no idea why
it was there. I'm wondering if there was another reason of that
function
other than just preventing out-of-bounds. Maybe chunfeng can answer
this?

We use @esit to prevent out-of-bounds array access. it's not a ring,
can't insert out-of-bounds value into head slot.

Thanks, so that function was only for out-of-bounds array access.
then I think we just can remove that function and use it as a ring.
Can you tell me _why_ it can't be used as a ring?

I think a transaction (e.g. esit_boundary = 7) can start its first SSPLIT
from Y_7 (offset = 7). But will that allocation be matched with this?

-               if ((offset + sch_ep->num_budget_microframes) > esit_boundary)
-                       break;

I mean I'm not sure why this is needed.

Until now, I couldn't find a way to accept the USB audio headset
with a configuration of { INT-IN 64 + ISOC-OUT 384 + ISOC-IN 192 }
without this patch.

quoted

Thanks!

quoted

thanks,

greg k-h

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