[U-Boot] [PATCH v2] usb: fix usb_stor_read/write on DM

Thu Jul 20 09:00:46 UTC 2017

On 07/20/2017 09:49 AM, Masahiro Yamada wrote:
> 2017-07-20 2:33 GMT+09:00 Marek Vasut <marex at denx.de>:
>> On 07/19/2017 05:38 PM, Masahiro Yamada wrote:
>>> 2017-07-15 21:57 GMT+09:00 Marek Vasut <marex at denx.de>:
>>>> On 07/15/2017 01:30 AM, Benoît Thébaudeau wrote:
>>>>> On Sat, Jul 15, 2017 at 12:06 AM, Marek Vasut <marex at denx.de> wrote:
>>>>>> On 07/14/2017 11:46 PM, Benoît Thébaudeau wrote:
>>>>>>> On Fri, Jul 14, 2017 at 1:50 PM, Marek Vasut <marex at denx.de> wrote:
>>>>>>>> On 07/14/2017 01:03 PM, Masahiro Yamada wrote:
>>>>>>>>> 2017-07-14 19:07 GMT+09:00 Marek Vasut <marex at denx.de>:
>>>>>>>>>> On 07/14/2017 04:31 AM, Masahiro Yamada wrote:
>>>>>>>>>>> Prior to DM, we could not enable different types of USB controllers
>>>>>>>>>>> at the same time.  DM was supposed to loosen the limitation.  It is
>>>>>>>>>>> true that we can compile drivers, but they do not work.
>>>>>>>>>>>
>>>>>>>>>>> For example, if EHCI is enabled, xHCI fails as follows:
>>>>>>>>>>>
>>>>>>>>>>>   => usb read 82000000 0 2000
>>>>>>>>>>>
>>>>>>>>>>>   USB read: device 0 block # 0, count 8192 ... WARN halted endpoint, queueing URB anyway.
>>>>>>>>>>>   Unexpected XHCI event TRB, skipping... (3fb54010 00000001 13000000 01008401)
>>>>>>>>>>>   BUG: failure at drivers/usb/host/xhci-ring.c:489/abort_td()!
>>>>>>>>>>>   BUG!
>>>>>>>>>>>   ### ERROR ### Please RESET the board ###
>>>>>>>>>>>
>>>>>>>>>>> The cause of the error seems the following code:
>>>>>>>>>>>
>>>>>>>>>>>   #ifdef CONFIG_USB_EHCI_HCD
>>>>>>>>>>>   /*
>>>>>>>>>>>    * The U-Boot EHCI driver can handle any transfer length as long as there is
>>>>>>>>>>>    * enough free heap space left, but the SCSI READ(10) and WRITE(10) commands are
>>>>>>>>>>>    * limited to 65535 blocks.
>>>>>>>>>>>    */
>>>>>>>>>>>   #define USB_MAX_XFER_BLK    65535
>>>>>>>>>>>   #else
>>>>>>>>>>>   #define USB_MAX_XFER_BLK    20
>>>>>>>>>>>   #endif
>>>>>>>>>>>
>>>>>>>>>>> To fix the problem, choose the chunk size at run-time for CONFIG_BLK.
>>>>>>>>>>
>>>>>>>>>> What happens if CONFIG_BLK is not set ?
>>>>>>>>>
>>>>>>>>> USB_MAX_XFER_BLK is chosen.
>>>>>>>>
>>>>>>>> And can we fix that even for non-CONFIG_BLK ?
>>>>>>>>
>>>>>>>>>> Why is it 20 for XHCI anyway ?
>>>>>>>>>
>>>>>>>>> You are the maintainer.
>>>>>>>>> (I hope) you have better knowledge with this.
>>>>>>>>
>>>>>>>> Heh, way to deflect the question. I seem to remember some discussion
>>>>>>>> about the DMA (?) limitation on XHCI, but I'd have to dig through the ML
>>>>>>>> archives myself.
>>>>>>>>
>>>>>>>>> Looks like the following commit was picked up by you.
>>>>>>>>
>>>>>>>> 5 years ago, way before DM was what it is today .
>>>>>>>
>>>>>>> And even way before the introduction of XHCI into U-Boot, which means
>>>>>>> that this 20 was targeting OHCI or proprietary HCDs, not XHCI.
>>>>>>> USB_MAX_READ_BLK was already set to 20 in the initial revision of
>>>>>>> usb_storage.c. As I said in the commit message, this 20 was certainly
>>>>>>> not optimal for these non-EHCI HCDs, but it restored the previous
>>>>>>> (i.e. pre-5dd95cf) behavior for these HCDs instead of using the 5 * 4
>>>>>>> KiB code, which was specific to ehci-hcd.c at that time. Without
>>>>>>> knowing the rationale for the legacy 20 blocks, the safest approach
>>>>>>> for non-EHCI HCDs was to use this value in order to avoid breaking a
>>>>>>> platform or something. Looking at ohci-hcd.c, it limits the transfer
>>>>>>> size to (N_URB_TD - 2) * 4 KiB, with N_URB_TD set to 48, so the
>>>>>>> maximum number of transfers would depend on the MSC block size.
>>>>>>> dwc2.c, isp116x-hcd.c, r8a66597-hcd.c, and sl811-hcd.c do not seem to
>>>>>>> have any limit caused by these drivers. The limit with the current
>>>>>>> XHCI code seems to be 64 * 64 KiB. So, nowadays, USB_MAX_XFER_BLK
>>>>>>> could be set to 65535 for all HCDs but OHCI and XHCI, which require
>>>>>>> specific rules depending on the MSC block size.
>>>>>>
>>>>>> For whatever reason, something tells me that setting the block size to
>>>>>> 64k for XHCI broke things, but I cannot locate the thread. But there's
>>>>>> something in the back of my head ...
>>>>>
>>>>> Indeed: according to what I said above, USB_MAX_XFER_BLK cannot be set
>>>>> to 65535 for XHCI. With an MSC block size of blksz = 512 bytes /
>>>>> block, USB_MAX_XFER_BLK can be set to at most 1 segment *
>>>>> (TRBS_PER_SEGMENT = 64 TRBs / segment) * (TRB_MAX_BUFF_SIZE = 65536
>>>>> bytes / TRB) / blksz = 8192 blocks for XHCI. And for OHCI, the limit
>>>>> is (N_URB_TD - 2 = 46 TDs) * (4096 bytes / TD) / blksz = 368 blocks.
>>>>> The buffer alignment may also have to be taken into account to adjust
>>>>> these values, which would require a USB_MAX_XFER_BLK(host_if, start,
>>>>> blksz) macro or function. USB_MAX_XFER_BLK can however be set to 65535
>>>>> regardless of blksz for all the other HCDs (i.e. EHCI, dwc2.c,
>>>>> isp116x-hcd.c, r8a66597-hcd.c, and sl811-hcd.c).
>>>>
>>>> That's probably what I was looking for, thanks.
>>>>
>>>
>>>
>>> So, how shall we handle this?
>>>
>>> If somebody can fix this in a correct way,
>>> I am happy to hand over this.
>>
>> Any way to fix it for !CONFIG_BLK ?
> 
> 
> common/usb_storage.c is sprinkled with ugly #ifdef CONFIG_BLK
> 
> IIUC, !CONFIG_BLK code will be removed after migration.
> 
> Is it worthwhile to save !CONFIG_BLK case?

Hmmmmmm, sigh. When is the migration happening, how far is it ?

-- 
Best regards,
Marek Vasut