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Subject: Re: [PATCH 2/2] usb-storage: revert from scsi_add_host_with_dma() to
 scsi_add_host()
To:     Tom Yan <tom.ty89@gmail.com>, hch@lst.de,
        gregkh@linuxfoundation.org, linux-usb@vger.kernel.org
Cc:     mathias.nyman@intel.com, linux-kernel@vger.kernel.org,
        linux-pci@vger.kernel.org, baolu.lu@linux.intel.com
References: <09992cec-65e4-2757-aae6-8fb02a42f961@redhat.com>
 <20201128154849.3193-1-tom.ty89@gmail.com>
 <20201128154849.3193-2-tom.ty89@gmail.com>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <5e62c383-22ea-6df6-5acc-5e9f381d4632@redhat.com>
Date:   Mon, 30 Nov 2020 10:50:48 +0100
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Hi,

On 11/28/20 4:48 PM, Tom Yan wrote:
> While the change only seemed to have caused issue on uas drives, we
> probably want to avoid it in the usb-storage driver as well, until
> we are sure it is the right thing to do.
> 
> Signed-off-by: Tom Yan <tom.ty89@gmail.com>

This seems to do a whole lot more then just dropping back from
 scsi_add_host_with_dma() to scsi_add_host(). This has way more
lines then the orginal commit.

IMHO it would be best to just revert commit 0154012f8018bba4d9971d1007c12ffd48539ddb
and then submit these changes as a separate patch (which would be
5.11 material then).

That separate patch could then also have a proper commit message
explaining the other changes you are making, which is also not
unimportant.

Regards,

Hans


> ---
>  drivers/usb/storage/scsiglue.c | 40 +++++++++++++++++-----------------
>  drivers/usb/storage/usb.c      |  3 +--
>  2 files changed, 21 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c
> index 560efd1479ba..6539bae1c188 100644
> --- a/drivers/usb/storage/scsiglue.c
> +++ b/drivers/usb/storage/scsiglue.c
> @@ -92,7 +92,7 @@ static int slave_alloc (struct scsi_device *sdev)
>  static int slave_configure(struct scsi_device *sdev)
>  {
>  	struct us_data *us = host_to_us(sdev->host);
> -	struct device *dev = sdev->host->dma_dev;
> +	struct device *dev = us->pusb_dev->bus->sysdev;
>  
>  	/*
>  	 * Many devices have trouble transferring more than 32KB at a time,
> @@ -120,6 +120,25 @@ static int slave_configure(struct scsi_device *sdev)
>  		 * better throughput on most devices.
>  		 */
>  		blk_queue_max_hw_sectors(sdev->request_queue, 2048);
> +	} else {
> +		/*
> +		 * Limit the total size of a transfer to 120 KB.
> +		 *
> +		 * Some devices are known to choke with anything larger. It seems like
> +		 * the problem stems from the fact that original IDE controllers had
> +		 * only an 8-bit register to hold the number of sectors in one transfer
> +		 * and even those couldn't handle a full 256 sectors.
> +		 *
> +		 * Because we want to make sure we interoperate with as many devices as
> +		 * possible, we will maintain a 240 sector transfer size limit for USB
> +		 * Mass Storage devices.
> +		 *
> +		 * Tests show that other operating have similar limits with Microsoft
> +		 * Windows 7 limiting transfers to 128 sectors for both USB2 and USB3
> +		 * and Apple Mac OS X 10.11 limiting transfers to 256 sectors for USB2
> +		 * and 2048 for USB3 devices.
> +		 */
> +		blk_queue_max_hw_sectors(sdev->request_queue, 240);
>  	}
>  
>  	/*
> @@ -627,25 +646,6 @@ static const struct scsi_host_template usb_stor_host_template = {
>  	.sg_tablesize =			SG_MAX_SEGMENTS,
>  
>  
> -	/*
> -	 * Limit the total size of a transfer to 120 KB.
> -	 *
> -	 * Some devices are known to choke with anything larger. It seems like
> -	 * the problem stems from the fact that original IDE controllers had
> -	 * only an 8-bit register to hold the number of sectors in one transfer
> -	 * and even those couldn't handle a full 256 sectors.
> -	 *
> -	 * Because we want to make sure we interoperate with as many devices as
> -	 * possible, we will maintain a 240 sector transfer size limit for USB
> -	 * Mass Storage devices.
> -	 *
> -	 * Tests show that other operating have similar limits with Microsoft
> -	 * Windows 7 limiting transfers to 128 sectors for both USB2 and USB3
> -	 * and Apple Mac OS X 10.11 limiting transfers to 256 sectors for USB2
> -	 * and 2048 for USB3 devices.
> -	 */
> -	.max_sectors =                  240,
> -
>  	/* emulated HBA */
>  	.emulated =			1,
>  
> diff --git a/drivers/usb/storage/usb.c b/drivers/usb/storage/usb.c
> index c2ef367cf257..f177da4ff1bc 100644
> --- a/drivers/usb/storage/usb.c
> +++ b/drivers/usb/storage/usb.c
> @@ -1050,8 +1050,7 @@ int usb_stor_probe2(struct us_data *us)
>  	usb_autopm_get_interface_no_resume(us->pusb_intf);
>  	snprintf(us->scsi_name, sizeof(us->scsi_name), "usb-storage %s",
>  					dev_name(dev));
> -	result = scsi_add_host_with_dma(us_to_host(us), dev,
> -					us->pusb_dev->bus->sysdev);
> +	result = scsi_add_host(us_to_host(us), dev);
>  	if (result) {
>  		dev_warn(dev,
>  				"Unable to add the scsi host\n");
>