linux-kernel - [PATCH 4/4] phy: usb: phy-brcm-usb-init: DRD mode can cause crash on startup

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Date:   Wed, 27 Dec 2017 14:28:51 -0500
From:   Al Cooper <alcooperx@...il.com>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Al Cooper <al.cooper@...adcom.com>,
        Al Cooper <alcooperx@...il.com>, linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com
Subject: [PATCH 4/4] phy: usb: phy-brcm-usb-init: DRD mode can cause crash on startup

From: Al Cooper <al.cooper@...adcom.com>

This is caused by a bug in the BDC core. When the BDC core comes
out of reset and it's not selected, it gets a backup clock. When
the BDC core is selected, it get's the main clock. If HOST mode
is then selected the BDC core has the main clock shut off but
the backup clock is not restored.

The failure scenario and cause are as follows:
- DRD mode is active
- Device mode is selected first in bootloader
- When host mode is now selected, the clock to the BDC is cut off.
- BDC registers are inaccessible and therefore the BDC driver
  crashes upon Linux boot.

The fix is to have the phy driver always force a BDC reset on
startup.

Fixes: 49859e55e364 ("phy: usb: phy-brcm-usb: Add Broadcom STB USB phy driver")
Signed-off-by: Al Cooper <alcooperx@...il.com>
---
 drivers/phy/broadcom/phy-brcm-usb-init.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/phy/broadcom/phy-brcm-usb-init.c b/drivers/phy/broadcom/phy-brcm-usb-init.c
index 6672adcc..1b7febc 100644
--- a/drivers/phy/broadcom/phy-brcm-usb-init.c
+++ b/drivers/phy/broadcom/phy-brcm-usb-init.c
@@ -918,6 +918,7 @@ void brcm_usb_init_common(struct brcm_usb_init_params *params)
 			USB_CTRL_UNSET_FAMILY(params, USB_PM, BDC_SOFT_RESETB);
 			break;
 		default:
+			USB_CTRL_UNSET_FAMILY(params, USB_PM, BDC_SOFT_RESETB);
 			USB_CTRL_SET_FAMILY(params, USB_PM, BDC_SOFT_RESETB);
 		break;
 		}
-- 
1.9.0.138.g2de3478