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

[Benoît Thébaudeau]

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).

Best regards,
Benoît