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

puneets
2012-03-01T12:59:29Z

Hi Marek,

On Thursday 01 March 2012 05:15 PM, Marek Vasut wrote:
> Hi!
>
>> 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.
> Well it does certainly not call usb_get_string()
>
Precisely, it avoids fetching string desc of 255 bytes. so better name
could be
"CONFIG_USB_AVOID_STRING_FETCH_255". Thanks for your comment.

>> 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.
> Cache alignment error ? Wow, how's that actually related to SUB string fetching?
> Maybe we should manually realign the result then? I still don't really
> understand what you're seeing, sorry ... can you please elaborate?
>
The particular mass storage device is -

Vendor: Kingston Rev: PMAP Prod: DataTraveler 2.0

Type: Removable Hard Disk

Capacity: 1906.0 MB = 1.8 GB (3903488 x 512)

When code tries to read Manufacturing Id..prod id...etc..it passes cache
aligned buffer "tbuf" in
"usb_string()" @usb.c. Inside "usb_string_sub()", usb_get_string()
passes as default 255 bytes to fetch string
descriptor.
The code in "ehci_submit_async() " invalidates *partially* the passed
buffer though we pass aligned buffer and "STD_ASS"
is received. Though it should invalidate only the cached line which is
equal(~32) to string desc length.

If we give delay of 1 ms after handshake() the cache alignment warning
does not spew...but delay of 1 ms is not acceptable.
So I enabled the code to fetch first string desc length and then fetch
string desc fetch, in this way the issue is resolved.
It makes sense also to fetch string desc length and then actual string
desc....

Thanks,
Puneet

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.
> Sure, I see your intention, but I still don't get the problem, see above. Can
> you also tell me if there's particular device that's broken and which one is it
> (precise type etc)?
>
> Thanks a lot for your cooperation on this matter!
>
> 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>

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