linux-kernel - SMSC9730 Autosuspend/Resume Questions

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Message-ID: <69e14429-a4d9-dd5c-5e70-c22086490cc0@exceet.de>
Date:   Wed, 17 Oct 2018 17:21:12 +0200
From:   Frieder Schrempf <frieder.schrempf@...eet.de>
To:     Steve Glendinning <steve.glendinning@...well.net>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Cc:     Oliver Neukum <oneukum@...e.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: SMSC9730 Autosuspend/Resume Questions

Hi,

I recently tested a board with SMSC9730 connected via USB HSIC to an 
i.MX6S SOC. I used these patches on top of v4.14-rc8 for the USB HSIC 
support: [1].

When I turned on autosuspend, the smsc95xx stopped in the middle of the 
suspending routine and 
/sys/bus/usb/devices/usb3/3-1/power/runtime_status reported "suspending" 
forever.

With some debug logs I found out, that the last line of code that was 
executed is [2], after that I didn't get any further messages.

Then I applied the following diff and the suspend/resume started to work 
reliably:

@@ -1382,10 +1385,11 @@ static int smsc95xx_link_ok_nopm(struct usbnet *dev)
         ret = smsc95xx_mdio_read_nopm(dev->net, mii->phy_id, MII_BMSR);
         if (ret < 0)
                 return ret;
-
+       /*
         ret = smsc95xx_mdio_read_nopm(dev->net, mii->phy_id, MII_BMSR);
         if (ret < 0)
                 return ret;
+       */

         return !!(ret & BMSR_LSTATUS);
  }

So it seems like the dummy read, that is commented with "first, a dummy 
read, needed to latch some MII phys" causes problems in my setup. Do you 
have an idea what could be the reason? Is this a proper fix?

Thanks,
Frieder

[1] https://patchwork.kernel.org/cover/10643089/
[2] 
https://github.com/torvalds/linux/blob/bab5c80b211035739997ebd361a679fa85b39465/drivers/net/usb/smsc95xx.c#L1382