From:   Stefan Wahren <stefan.wahren@i2se.com>
Subject: [BUG] mt76x0u: Probing issues on Raspberry Pi 3 B+
To:     Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Cc:     Stanislaw Gruszka <sgruszka@redhat.com>,
        Felix Fietkau <nbd@nbd.name>,
        Doug Anderson <dianders@chromium.org>,
        Minas Harutyunyan <hminas@synopsys.com>,
        linux-wireless <linux-wireless@vger.kernel.org>,
        linux-usb@vger.kernel.org
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 <20190211074455.GA6292@redhat.com>
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Message-ID: <500c0d4a-611a-1b00-5ea4-7368e5e9f1e9@i2se.com>
Date:   Mon, 11 Feb 2019 16:27:40 +0100
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Hi,

Am 11.02.19 um 16:10 schrieb Lorenzo Bianconi:
>> Hi Lorenzo,
>>
>> Am 11.02.19 um 12:06 schrieb Lorenzo Bianconi:
>>>> Hi,
>>>>
>>>> Am 11.02.19 um 11:04 schrieb Lorenzo Bianconi:
>>>>>> On Sun, Feb 10, 2019 at 11:22:25AM +0100, Lorenzo Bianconi wrote:
>>>>>>>> On Sat, Feb 09, 2019 at 09:29:05PM +0100, Stefan Wahren wrote:
>>>>>>>>>> could you please test the following series:
>>>>>>>>>> https://patchwork.kernel.org/cover/10764453/
>>>>>>>>> yeah this fixed the probing timeout and the driver will probe successful. AFAIK the dwc2 host mode doesn't support scatter-gather yet.
>>>>>>>> So this is either dwc2 scatter-gather problem which should be addressed in
>>>>>>>> this driver or mt76x0u does something wrong when configuring SG.
>>>>>>>>
>>>>>>>> Disabling SG is just workaround, which do not address actual problem.
>>>>>>>>
>>>>>>>> I think I found mt76x0u issue that could cause this USB probe error
>>>>>>>> (and possibly also address AMD IOMMU issue). We seems do not correctly
>>>>>>>> set URB transfer length smaller than sg buffer length. Attached  patch
>>>>>>>> should correct that.
>>>>>>> Hi Stanislaw,
>>>>>>>
>>>>>>> I think 'sg[0].length' is already set in mt76u_fill_rx_sg().
>>>>>> It is, buf->len and sg[0].length are initialized to the same value for 1
>>>>>> segment. But then buf->len (assigned to urb->buffer_transfer_length) change
>>>>>> to smaller value , but sg[0].length stay the same. What I think can be
>>>>>> problem for usb host driver.
>>>>>>
>>>>>>> Moreover applying this patch I got the following crash (rpi-5.0.y):
>>>>>> Ok, so with patch probe fail instantly and trigger yet another bug(s)
>>>>>> on error path. You seems to address that already. 
>>>>>>
>>>>>>> Moreover for mt76x0u SG is 'already' disabled since we use just one
>>>>>>> buffer so from performance point of view I do not see any difference
>>>>>>> of using a standard usb buffer.
>>>>>>> This patch has been tested in multiple scenarios and seems to fix
>>>>>>> reported issues (for usb2.0).
>>>>>> Ok, so passing buffer via urb->transfer_buffer works. But why urb->sg
>>>>>> does not work for 1 segment ?
>>>>> Here it is a different issue respect to the AMD IOMMU one, dwc2 host driver
>>>>> does not implement SG I/O so probing fails. I guess it is still useful to
>>>>> implement a 'legacy' mode that enable mt76 on host controllers that do not implement
>>>>> SG I/O (rpi is a very common device so it will be cool to have mt76 working on
>>>>> it). Moreover we are not removing functionalities, user experience will remain
>>>>> the same
>>>>>
>>>> i'm not sure that you understand my mail [1] with the summary of my test
>>>> results.
>>>>
>>> Yes right, I did not get it sorry :)
>>> as indicated here https://www.raspberrypi.org/documentation/linux/kernel/building.md
>>> I am using bcm2709_defconfig config (using it I spotted the mt76 crashes and
>>> probe failure)
>> no problem, at the beginning this could be very confusing. I only want
>> to clarify that this documentation refers to the vendor kernel (with a
>> different USB host driver) of the Raspberry Pi Foundation.
>>
>> All my results refers to the mainline kernel we all should talk about. I
>> started a gist which try to describe the mainline variant:
>> https://gist.github.com/lategoodbye/c7317a42bf7f9c07f5a91baed8c68f75
> So to summarize:
> - Raspberry Pi Foundation kernel works just with RFC series
> - mainline kernel works out of the box
>
> is my understanding correct? 

not really.

Compiling the mainline kernel with arm/multi_v7_defconfig it works.
Using the same kernel but with arm64/defconfig doesn't work. But i don't
think this is a 32/64 bit issue. The arm64 defconfig is much more
complex (e.g. enables more IOMMU stuff).

Regards
Stefan