linux-kernel - [PATCH v2 1/5] usb: gadget: f_uac2: always increase endpoint max_packet

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Date:   Mon,  1 Mar 2021 13:49:31 +0200
From:   Ruslan Bilovol <ruslan.bilovol@...il.com>
To:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ruslan Bilovol <ruslan.bilovol@...il.com>,
        Peter Chen <peter.chen@...escale.com>, <stable@...r.kernel.org>
Subject: [PATCH v2 1/5] usb: gadget: f_uac2: always increase endpoint max_packet_size by one audio slot

As per UAC2 Audio Data Formats spec (2.3.1.1 USB Packets),
if the sampling rate is a constant, the allowable variation
of number of audio slots per virtual frame is +/- 1 audio slot.

It means that endpoint should be able to accept/send +1 audio
slot.

Previous endpoint max_packet_size calculation code
was adding sometimes +1 audio slot due to DIV_ROUND_UP
behaviour which was rounding up to closest integer.
However this doesn't work if the numbers are divisible.

It had no any impact with Linux hosts which ignore
this issue, but in case of more strict Windows it
caused rejected enumeration

Thus always add +1 audio slot to endpoint's max packet size

Fixes: 913e4a90b6f9 ("usb: gadget: f_uac2: finalize wMaxPacketSize according to bandwidth")
Cc: Peter Chen <peter.chen@...escale.com>
Cc: <stable@...r.kernel.org> #v4.3+
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@...il.com>
---
 drivers/usb/gadget/function/f_uac2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
index 740cb64..c62cccb 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -478,7 +478,7 @@ static int set_ep_max_packet_size(const struct f_uac2_opts *uac2_opts,
 	}
 
 	max_size_bw = num_channels(chmask) * ssize *
-		DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1)));
+		((srate / (factor / (1 << (ep_desc->bInterval - 1)))) + 1);
 	ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,
 						    max_size_ep));
 
-- 
1.9.1