linux-kernel - Re: Why is the max

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Date:   Sat, 24 Sep 2016 09:54:22 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Lipengcheng <lpc.li@...ilicon.com>
cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "usb-storage@...ts.one-eyed-alien.net" 
        <usb-storage@...ts.one-eyed-alien.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Fangzhuanghai <fangzhuanghai@...ilicon.com>,
        Caizhiyong <caizhiyong@...ilicon.com>
Subject: Re: Why is the max_sectors set the 240

On Sat, 24 Sep 2016, Lipengcheng wrote:

> Hi,
> Some special superspeed u3 disk connect xhci control. Then the u3
> disk is read/write and has the Transfer error on endpoint
> (COMP_TX_ERR) error. However in the pc windows does not have the
> problem.By analysis, the windows is each transfer 64K size. The Linux
> is 120K size. In the scsiglue.c, the max_sectors value set the 128
> and each transfer 64K size. Then the Linux system is no problem too.
> Why is the max_sectors set the 240?  May the max_sectors be the other
> values?

Most devices work okay with max_sectors set to 240.  However, you can 
change the value if you want.  Read the usb-storage.quirks section in 
Documentation/kernel-parameters.txt; the m flag will set max_sectors to 
64.

Alan Stern