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

[puneets <puneets@nvidia.com>]

Hi Marek,
On Thursday 01 March 2012 02:59 AM, Marek Vasut wrote:
>> 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
>
It does not avoid string fetch.
I checked with few mass storage devices that they does not handle string 
descriptor request correctly and so we get
start/stop Cache alignment error. One way is, blacklist those devices by 
vendor id/product id..
etc. This is done in Linux kernel. Plz see Message.c (drivers\usb\core) 
Line: 722.
Blacklisting the device requires a framework to detect the 
device...However this could be achieved
simply with this implementation.

>> +	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>


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