linux-kernel - [PATCH v4 2/2] usb: overridable hub bInterval by device node

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Date:   Tue,  3 Dec 2019 18:15:52 +0800
From:   Ikjoon Jang <ikjn@...omium.org>
To:     linux-usb@...r.kernel.org
Cc:     GregKroah-Hartman <gregkh@...uxfoundation.org>,
        RobHerring <robh+dt@...nel.org>,
        MarkRutland <mark.rutland@....com>,
        AlanStern <stern@...land.harvard.edu>,
        SuwanKim <suwan.kim027@...il.com>,
        "GustavoA . R . Silva" <gustavo@...eddedor.com>,
        IkjoonJang <ikjn@...omium.org>, JohanHovold <johan@...nel.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        drinkcat@...omium.org
Subject: [PATCH v4 2/2] usb: overridable hub bInterval by device node

This patch enables hub device to override its own endpoint descriptor's
bInterval when the hub has a device node with "hub,interval" property.

When we know reducing autosuspend delay for built-in HIDs is better for
power saving, we can reduce it to the optimal value. But if a parent hub
has a long bInterval, mouse lags a lot from more frequent autosuspend.
So this enables overriding bInterval for a hard wired hub device only
when we know that reduces the power consumption.

Signed-off-by: Ikjoon Jang <ikjn@...omium.org>
Acked-by: Alan Stern <stern@...land.harvard.edu>
---
 drivers/usb/core/config.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index 5f40117e68e7..95ec5af42a1c 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -6,6 +6,7 @@
 #include <linux/usb.h>
 #include <linux/usb/ch9.h>
 #include <linux/usb/hcd.h>
+#include <linux/usb/of.h>
 #include <linux/usb/quirks.h>
 #include <linux/module.h>
 #include <linux/slab.h>
@@ -257,6 +258,14 @@ static int usb_parse_endpoint(struct device *ddev, int cfgno, int inum,
 	memcpy(&endpoint->desc, d, n);
 	INIT_LIST_HEAD(&endpoint->urb_list);
 
+	/* device node property overrides bInterval */
+	if (usb_of_has_combined_node(to_usb_device(ddev))) {
+		u32 interval = 0;
+		if (!of_property_read_u32(ddev->of_node, "hub,interval",
+				    &interval))
+			d->bInterval = min_t(u8, interval, 255);
+	}
+
 	/*
 	 * Fix up bInterval values outside the legal range.
 	 * Use 10 or 8 ms if no proper value can be guessed.
-- 
2.24.0.393.g34dc348eaf-goog