[U-Boot] [PATCH v3 2/2] usb: Add CONFIG to fetch string descriptor

[Marek Vasut <marex@denx.de>]

> Add "CONFIG_USB_STRING_FETCH" to fetch first string descriptor length
> and then pass this length to fetch string descriptor.
> 
> Signed-off-by: Puneet Saxena <puneets@nvidia.com>
> ---
> 
> Changes for V2:
>    - Change existing config by "CONFIG_USB_STRING_FETCH"
> 
> Changes for V3:
>     - Removed extra new line
>     - Explained "CONFIG_USB_STRING_FETCH" in top level README
> 
>  README                          |    4 ++++
>  common/usb.c                    |    4 ++++
>  include/configs/tegra2-common.h |    2 ++
>  3 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/README b/README
> index 7adf7c7..c045a37 100644
> --- a/README
> +++ b/README
> @@ -1138,6 +1138,10 @@ The following options need to be configured:
>  		CONFIG_USB_EHCI_TXFIFO_THRESH enables setting of the
>  		txfilltuning field in the EHCI controller on reset.
> 
> +		CONFIG_USB_STRING_FETCH
> +		Enables settings to USB core to handle string issues which
> +		few devices can not handle.
> +
>  - USB Device:
>  		Define the below if you wish to use the USB console.
>  		Once firmware is rebuilt from a serial console issue the
> diff --git a/common/usb.c b/common/usb.c
> index 191bc5b..a73cb60 100644
> --- a/common/usb.c
> +++ b/common/usb.c
> @@ -658,9 +658,13 @@ static int usb_string_sub(struct usb_device *dev,
> unsigned int langid, {
>  	int rc;
> 
> +#ifdef CONFIG_USB_STRING_FETCH

Shouldn't this be something like ... CONFIG_USB_AVOID_STRING_FETCH then?

Anyway, how come some devices can't handle it? What happens then? What devices 
are those (exact type etc)?

I believe the bug is deeper and adding extra config options can be avoided, what 
do you think?

Thanks!

M

> +	rc = -1;
> +#else
>  	/* Try to read the string descriptor by asking for the maximum
>  	 * possible number of bytes */
>  	rc = usb_get_string(dev, langid, index, buf, 255);
> +#endif
> 
>  	/* If that failed try to read the descriptor length, then
>  	 * ask for just that many bytes */
> diff --git a/include/configs/tegra2-common.h
> b/include/configs/tegra2-common.h index 266d0e5..d20b49c 100644
> --- a/include/configs/tegra2-common.h
> +++ b/include/configs/tegra2-common.h
> @@ -93,6 +93,8 @@
>  #define CONFIG_USB_EHCI_TXFIFO_THRESH	10
>  #define CONFIG_EHCI_IS_TDI
>  #define CONFIG_EHCI_DCACHE
> +/* string descriptors must not be fetched using a 255-byte read */
> +#define CONFIG_USB_STRING_FETCH
> 
>  /* include default commands */
>  #include <config_cmd_default.h>