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

Thu Jul 20 09:38:36 UTC 2017

+Simon,

On Thu, Jul 20, 2017 at 5:00 PM, Marek Vasut <marex at denx.de> wrote:
> 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 ?

One idea is to force all board to switch to driver model at a preset
timeline. After the deadline, boards do not switch to DM will get
dropped by the mainline. I noticed that not all boards are actively
maintained...

Regards,
Bin