linux-kernel - [PATCH] USB: MAX3421: Handle USB NAK correctly

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Message-Id: <20230127024734.8777-1-mark.tomlinson@alliedtelesis.co.nz>
Date:   Fri, 27 Jan 2023 15:47:34 +1300
From:   Mark Tomlinson <mark.tomlinson@...iedtelesis.co.nz>
To:     gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mark Tomlinson <mark.tomlinson@...iedtelesis.co.nz>
Subject: [PATCH] USB: MAX3421: Handle USB NAK correctly

A USB peripheral can respond with a NAK if it is not yet ready to
send/receive data. In this case, the transaction should be retried. The
MAX3421 driver did do this, and switched to a different type of retry
after a number of 'fast' retries. On at least some USB flash devices,
this second type of retry never succeeds. This patch changes the
behaviour so that 'fast' retries continue.

Signed-off-by: Mark Tomlinson <mark.tomlinson@...iedtelesis.co.nz>
---
 drivers/usb/host/max3421-hcd.c | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/drivers/usb/host/max3421-hcd.c b/drivers/usb/host/max3421-hcd.c
index 352e3ac2b377..9a87056fc738 100644
--- a/drivers/usb/host/max3421-hcd.c
+++ b/drivers/usb/host/max3421-hcd.c
@@ -72,12 +72,6 @@
 #define USB_MAX_FRAME_NUMBER	0x7ff
 #define USB_MAX_RETRIES		3 /* # of retries before error is reported */
 
-/*
- * Max. # of times we're willing to retransmit a request immediately in
- * resposne to a NAK.  Afterwards, we fall back on trying once a frame.
- */
-#define NAK_MAX_FAST_RETRANSMITS	2
-
 #define POWER_BUDGET	500	/* in mA; use 8 for low-power port testing */
 
 /* Port-change mask: */
@@ -924,11 +918,8 @@ max3421_handle_error(struct usb_hcd *hcd, u8 hrsl)
 		 * Device wasn't ready for data or has no data
 		 * available: retry the packet again.
 		 */
-		if (max3421_ep->naks++ < NAK_MAX_FAST_RETRANSMITS) {
-			max3421_next_transfer(hcd, 1);
-			switch_sndfifo = 0;
-		} else
-			max3421_slow_retransmit(hcd);
+		max3421_next_transfer(hcd, 1);
+		switch_sndfifo = 0;
 		break;
 	}
 	if (switch_sndfifo)
-- 
2.39.1