linux-kernel - Re: [PATCH] drivers: usb: fsl: Workaround for USB erratum-A005275

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Date:	Fri, 31 Jul 2015 12:33:53 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Nikhil Badola <nikhil.badola@...escale.com>
cc:	linux-kernel@...r.kernel.org, <linux-usb@...r.kernel.org>,
	<gregkh@...uxfoundation.org>,
	Ramneek Mehresh <ramneek.mehresh@...escale.com>
Subject: Re: [PATCH] drivers: usb: fsl: Workaround for USB erratum-A005275

On Fri, 31 Jul 2015, Nikhil Badola wrote:

> Incoming packets in high speed are randomly corrupted by h/w
> resulting in multiple errors. This workaround makes FS as
> default mode in all affected socs by disabling HS chirp
> signalling.This errata does not affect FS and LS mode.
> 
> Forces all HS devices to connect in FS mode for all socs
> affected by this erratum:
> P3041 and P2041 rev 1.0 and 1.1
> P5020 and P5010 rev 1.0 and 2.0
> P5040, P1010 and T4240 rev 1.0

Ooh, that's a really bad bug.  People will be pretty annoyed that they 
can't use high speed connections.

> --- a/drivers/usb/host/ehci-hub.c
> +++ b/drivers/usb/host/ehci-hub.c
> @@ -1222,6 +1222,13 @@ int ehci_hub_control(
>  				ehci->reset_done [wIndex] = jiffies
>  						+ msecs_to_jiffies (50);
>  			}
> +
> +			/* Force full-speed connect for FSL high-speed erratum;
> +			 * disable HS Chirp by setting PFSC bit
> +			 */
> +			if (ehci_has_fsl_hs_errata(ehci))
> +				temp |= (1 << PORTSC_FSL_PFSC);
> +

This hunk was added in the wrong place.  It should come before the 
closing '}' above, not after.  That's because you don't want to force a 
full-speed connection if the device is already using low speed.

> --- a/drivers/usb/host/ehci.h
> +++ b/drivers/usb/host/ehci.h
> @@ -215,6 +215,7 @@ struct ehci_hcd {			/* one per controller */
>  	/* SILICON QUIRKS */
>  	unsigned		no_selective_suspend:1;
>  	unsigned		has_fsl_port_bug:1; /* FreeScale */
> +	unsigned		has_fsl_hs_errata:1;	/* Freescale HS quirk */
>  	unsigned		big_endian_mmio:1;
>  	unsigned		big_endian_desc:1;
>  	unsigned		big_endian_capbase:1;
> @@ -675,6 +676,17 @@ ehci_port_speed(struct ehci_hcd *ehci, unsigned int portsc)
>  #define	ehci_port_speed(ehci, portsc)	USB_PORT_STAT_HIGH_SPEED
>  #endif
>  
> +#define PORTSC_FSL_PFSC	24	/* Port Force Full-Speed Connect */
> +
> +#if defined(CONFIG_PPC_85xx)
> +/* Some Freescale processors have an erratum (USB A-005275) in which
> + * incoming packets get corrupted in HS mode
> + */
> +#define ehci_has_fsl_hs_errata(e)	((e)->has_fsl_hs_errata)
> +#else
> +#define ehci_has_fsl_hs_errata(e)	(0)
> +#endif
> +
>  /*-------------------------------------------------------------------------*/

I would prefer it if you add your new hunk after this /*-----...---*/ 
dividing line (that is, next to the ehci_has_fsl_portno_bug() code) 
instead of before the dividing line.

Otherwise this looks okay.

Alan Stern

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