From: Roger Quadros <rogerq@ti.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: <linux-arm-kernel@lists.infradead.org>,
Alan Stern <stern@rowland.harvard.edu>,
Felipe Balbi <balbi@kernel.org>,
Grygorii Strashko <grygorii.strashko@ti.com>,
Stuart Yoder <stuart.yoder@nxp.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
Sekhar Nori <nsekhar@ti.com>,
Russell King - ARM Linux <linux@armlinux.org.uk>,
lkml <linux-kernel@vger.kernel.org>,
Scott Wood <oss@buserror.net>,
David Fisher <david.fisher1@synopsys.com>,
"Thang Q. Nguyen" <tqnguyen@apm.com>, Leo Li <pku.leo@gmail.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev
Date: Wed, 7 Sep 2016 16:04:52 +0300 [thread overview]
Message-ID: <632cd67b-34de-2177-529f-e1437924bae2@ti.com> (raw)
In-Reply-To: <8802454.xFheq55hVP@wuerfel>
On 07/09/16 11:29, Arnd Bergmann wrote:
> On Wednesday, September 7, 2016 10:17:31 AM CEST Roger Quadros wrote:
>>>
>>> Speaking of that flag, I suppose we need the same logic to know where
>>> to look for USB devices attached to a dwc3 host when we need to describe
>>> them in DT. By default we look for child device nodes under the
>>> node of the HCD device node, but that would be wrong here too.
>>
>> I didn't get this part. Information about USB devices attached to a USB host
>> is never provided in DT because they are always dynamically created via
>> usb_new_device(), whether they are hard-wired on the board or hot-plugged.
>>
>> These USB devices inherit their DMA masks in the usb_alloc_dev() routine
>> whereas each interface within the USB device inherits its DMA mask in
>> usb_set_configuration().
>
> We had talked about adding support for this for at least six years (probably
> much more), but Peter Chen finally added it this year in commit 69bec72598
> ("USB: core: let USB device know device node").
OK. Thanks for this pointer.
>
> The main use for it is to let you specify a MAC address for on-board
> ethernet devices that lack an EPROM, but any other information can be
> added that way too.
>
>> There is a bug in the USB core because of which the ISB device and interfaces
>> do not inherit dma_pfn_offset correctly for which I've sent a patch
>> https://lkml.org/lkml/2016/8/17/275
>
> I'm a bit skeptical about this. Clearly if we set the dma_mask, we should
> also set the dma_pfn_offset, but what exactly is this used for in USB
> devices?
Consider the mass storage device case.
USB storage driver creates a scsi host for the mass storage interface in
drivers/usb/storage/usb.c
The scsi host parent device is nothing but the the USB interface device.
Now, __scsi_init_queue() calls scsi_calculate_bounce_limit() to find out
and set the block layer bounce limit.
scsi_calculate_bounce_limit() uses dma_max_pfn(host_dev) to get the bounce_limit.
host_dev is nothing but the device representing the mass storage interface.
If that device doesn't have the right dma_pfn_offset, then dma_max_pfn()
is messed up and the bounce buffer limit is wrong.
>
> As I understand it, the dma_mask/dma_pfn_offset etc is used for the DMA
> mapping interface, but that can't really be used on USB devices, which
> I assume use usb_alloc_coherent() and the URB interfaces for passing data
> between a USB driver and the HCD. My knowledge of USB device drivers
> is a bit lacking, so it's possible I'm misunderstanding things here.
>
cheers,
-roger
next prev parent reply other threads:[~2016-09-07 13:06 UTC|newest]
Thread overview: 91+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-25 19:21 [PATCH] usb: dwc3: host: inherit dma configuration from parent dev Grygorii Strashko
2016-04-26 6:17 ` Felipe Balbi
2016-04-26 8:14 ` Grygorii Strashko
2016-04-27 5:41 ` Felipe Balbi
2016-04-27 11:55 ` Grygorii Strashko
2016-04-27 13:59 ` Catalin Marinas
2016-04-27 14:11 ` Arnd Bergmann
2016-04-27 15:50 ` Catalin Marinas
2016-04-27 16:04 ` Arnd Bergmann
2016-04-27 16:53 ` Felipe Balbi
2016-04-27 17:42 ` Arnd Bergmann
2016-04-27 17:59 ` Alan Stern
2016-04-27 18:08 ` Arnd Bergmann
2016-04-27 20:05 ` Felipe Balbi
2016-04-27 21:05 ` Arnd Bergmann
2016-04-28 6:37 ` Felipe Balbi
2016-04-28 14:16 ` Russell King - ARM Linux
2016-04-28 14:23 ` Arnd Bergmann
2016-04-28 14:27 ` Felipe Balbi
2016-09-01 22:14 ` Leo Li
2016-09-02 10:43 ` Arnd Bergmann
2016-09-02 10:47 ` Russell King - ARM Linux
2016-09-02 11:08 ` Felipe Balbi
2016-09-02 14:11 ` Felipe Balbi
2016-09-02 14:21 ` Alan Stern
2016-09-02 15:51 ` Arnd Bergmann
2016-09-07 7:17 ` Roger Quadros
2016-09-07 8:29 ` Arnd Bergmann
2016-09-07 13:04 ` Roger Quadros [this message]
2016-09-07 14:38 ` Arnd Bergmann
2016-09-02 16:23 ` Grygorii Strashko
2016-09-02 10:53 ` Felipe Balbi
2016-09-02 11:55 ` Robin Murphy
2016-09-02 12:56 ` Felipe Balbi
2016-09-02 13:10 ` Arnd Bergmann
2016-09-02 22:16 ` Leo Li
2016-09-05 15:39 ` Arnd Bergmann
2016-09-06 6:35 ` Peter Chen
2016-09-06 6:40 ` Felipe Balbi
2016-09-06 10:46 ` Arnd Bergmann
2016-09-06 10:50 ` Felipe Balbi
2016-09-06 13:27 ` Arnd Bergmann
2016-09-07 6:51 ` Felipe Balbi
2016-09-07 7:44 ` Peter Chen
2016-09-07 8:52 ` Arnd Bergmann
2016-09-07 9:29 ` Peter Chen
2016-09-07 9:35 ` Russell King - ARM Linux
2016-09-07 10:18 ` Felipe Balbi
2016-09-06 10:38 ` Arnd Bergmann
2016-09-07 6:33 ` Peter Chen
2016-09-07 8:48 ` Arnd Bergmann
2016-09-07 9:55 ` Peter Chen
2016-09-07 10:33 ` Robin Murphy
2016-09-07 10:47 ` Felipe Balbi
2016-09-14 16:31 ` Lorenzo Pieralisi
2016-09-14 21:50 ` Arnd Bergmann
2016-09-07 10:24 ` Felipe Balbi
2016-09-07 15:24 ` Arnd Bergmann
2016-09-07 16:08 ` Alan Stern
2016-09-07 19:45 ` Arnd Bergmann
2016-09-08 1:15 ` Peter Chen
2016-09-08 8:02 ` Arnd Bergmann
2016-09-08 8:03 ` Felipe Balbi
2016-09-08 8:26 ` Arnd Bergmann
2016-09-08 8:29 ` Felipe Balbi
2016-09-08 8:45 ` Arnd Bergmann
2016-09-08 9:43 ` Felipe Balbi
2016-09-08 10:17 ` Arnd Bergmann
2016-09-08 11:00 ` Felipe Balbi
2016-09-08 11:11 ` Arnd Bergmann
2016-09-08 11:20 ` Felipe Balbi
2016-09-08 11:39 ` Arnd Bergmann
2016-09-08 11:52 ` Felipe Balbi
2016-09-08 12:46 ` Arnd Bergmann
2016-09-08 12:02 ` Grygorii Strashko
2016-09-08 12:14 ` Arnd Bergmann
2016-09-08 12:28 ` Peter Chen
2016-09-08 12:52 ` Arnd Bergmann
2016-09-09 1:37 ` Peter Chen
2016-09-08 12:59 ` Grygorii Strashko
2016-09-09 1:52 ` Peter Chen
2016-09-21 11:06 ` Sriram Dash
2016-09-21 11:31 ` Arnd Bergmann
2016-09-21 11:43 ` Sriram Dash
2016-09-21 12:48 ` Arnd Bergmann
2016-09-22 5:02 ` Sriram Dash
2016-10-07 22:46 ` Leo Li
2016-09-21 17:14 ` [PATCH] usb: xhci: Fix the patch inherit dma configuration from kbuild test robot
2016-04-27 20:57 ` [PATCH] usb: dwc3: host: inherit dma configuration from parent dev Felipe Balbi
2016-04-27 14:14 ` Grygorii Strashko
2016-05-05 17:07 ` Brian Norris
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