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Subject: Re: [PATCH 1/2] uas: revert from scsi_add_host_with_dma() to
 scsi_add_host()
To:     Tom Yan <tom.ty89@gmail.com>,
        Alan Stern <stern@rowland.harvard.edu>
Cc:     Christoph Hellwig <hch@lst.de>,
        Greg KH <gregkh@linuxfoundation.org>,
        linux-usb <linux-usb@vger.kernel.org>,
        Mathias Nyman <mathias.nyman@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-pci@vger.kernel.org, Lu Baolu <baolu.lu@linux.intel.com>
References: <09992cec-65e4-2757-aae6-8fb02a42f961@redhat.com>
 <20201128154849.3193-1-tom.ty89@gmail.com>
 <62e0d5ea-e665-b913-5482-a75db0ac1368@redhat.com>
 <CAGnHSE=sS7tvttuTwE_s+QbCUVCfhmHnuXQp1g1AkZ=JEoxmQA@mail.gmail.com>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <899cea7f-b306-0ce4-06e9-aa5d083573cb@redhat.com>
Date:   Tue, 1 Dec 2020 12:09:54 +0100
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Hi,

On 11/30/20 8:30 PM, Tom Yan wrote:
> Hmm, I wonder if I/we wrongly assumed that the dma_dev used for the
> hw_max_sectors clamping in __scsi_init_queue() is wrong.
> 
> So instead of adding a fallback else-clause here or using "sysdev" as
> dma_dev like in the current upstream code, maybe we should actually do
> a three-way min: the "changed" hw_max_sectors, dma_max_mapping_size of
> dma_dev("dev") and dma_max_mapping_size of sysdev...?

So both here and in the 2/2 patch thread there are lots of open questions,
which to me suggests that for 5.10 we really should just go with the 3 reverts
which I suggested earlier.

Regards,

Hans


> 
> On Mon, 30 Nov 2020 at 17:48, Hans de Goede <hdegoede@redhat.com> wrote:
>>
>> Hi,
>>
>> On 11/28/20 4:48 PM, Tom Yan wrote:
>>> Apparently the former (with the chosen dma_dev) may cause problem in certain
>>> case (e.g. where thunderbolt dock and intel iommu are involved). The error
>>> observed was:
>>>
>>> XHCI swiotlb buffer is full / DMAR: Device bounce map failed
>>>
>>> For now we retain the clamp for hw_max_sectors against the dma_max_mapping_size.
>>> Since the device/size for the clamp that is applied when the scsi request queue
>>> is initialized/allocated is different than the one used here, we invalidate the
>>> early clamping by making a fallback blk_queue_max_hw_sectors() call.
>>>
>>> Signed-off-by: Tom Yan <tom.ty89@gmail.com>
>>
>> I can confirm that this fixes the network performance on a Lenovo Thunderbolt
>> dock generation 2, which uses an USB attach NIC.
>>
>> With this patch added on top of 5.10-rc5 scp performance to another machine
>> on the local gbit LAN goes back from the regressed 1 MB/s to its original 100MB/s
>> as it should be:
>>
>> Tested-by: Hans de Goede <hdegoede@redhat.com>
>>
>> Regards,
>>
>> Hans
>>
>>
>>> ---
>>>  drivers/usb/storage/uas.c | 11 +++++++----
>>>  1 file changed, 7 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
>>> index c8a577309e8f..5db1325cea20 100644
>>> --- a/drivers/usb/storage/uas.c
>>> +++ b/drivers/usb/storage/uas.c
>>> @@ -843,18 +843,21 @@ static int uas_slave_alloc(struct scsi_device *sdev)
>>>  static int uas_slave_configure(struct scsi_device *sdev)
>>>  {
>>>       struct uas_dev_info *devinfo = sdev->hostdata;
>>> -     struct device *dev = sdev->host->dma_dev;
>>> +     struct usb_device *udev = devinfo->udev;
>>>
>>>       if (devinfo->flags & US_FL_MAX_SECTORS_64)
>>>               blk_queue_max_hw_sectors(sdev->request_queue, 64);
>>>       else if (devinfo->flags & US_FL_MAX_SECTORS_240)
>>>               blk_queue_max_hw_sectors(sdev->request_queue, 240);
>>> -     else if (devinfo->udev->speed >= USB_SPEED_SUPER)
>>> +     else if (udev->speed >= USB_SPEED_SUPER)
>>>               blk_queue_max_hw_sectors(sdev->request_queue, 2048);
>>> +     else
>>> +             blk_queue_max_hw_sectors(sdev->request_queue,
>>> +                                      SCSI_DEFAULT_MAX_SECTORS);
>>>
>>>       blk_queue_max_hw_sectors(sdev->request_queue,
>>>               min_t(size_t, queue_max_hw_sectors(sdev->request_queue),
>>> -                   dma_max_mapping_size(dev) >> SECTOR_SHIFT));
>>> +                   dma_max_mapping_size(udev->bus->sysdev) >> SECTOR_SHIFT));
>>>
>>>       if (devinfo->flags & US_FL_NO_REPORT_OPCODES)
>>>               sdev->no_report_opcodes = 1;
>>> @@ -1040,7 +1043,7 @@ static int uas_probe(struct usb_interface *intf, const struct usb_device_id *id)
>>>       shost->can_queue = devinfo->qdepth - 2;
>>>
>>>       usb_set_intfdata(intf, shost);
>>> -     result = scsi_add_host_with_dma(shost, &intf->dev, udev->bus->sysdev);
>>> +     result = scsi_add_host(shost, &intf->dev);
>>>       if (result)
>>>               goto free_streams;
>>>
>>>
>>
>