linux-kernel - RE: [PATCH] usb: gadget: Add the console support for usb-to-serial port

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Date:	Wed, 18 Nov 2015 12:05:59 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Baolin Wang' <baolin.wang@...aro.org>,
	Andy Shevchenko <andy.shevchenko@...il.com>
CC:	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"r.baldyga@...sung.com" <r.baldyga@...sung.com>,
	"fabio.estevam@...escale.com" <fabio.estevam@...escale.com>,
	Philip Oberstaller <Philip.Oberstaller@...tentrio.com>,
	Peter Hurley <peter@...leysoftware.com>,
	"scottwood@...escale.com" <scottwood@...escale.com>,
	Mark Brown <broonie@...nel.org>,
	USB <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] usb: gadget: Add the console support for usb-to-serial
 port

From: Baolin Wang
> Sent: 18 November 2015 10:45
> On 18 November 2015 at 17:32, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > On Wed, Nov 18, 2015 at 4:15 AM, Baolin Wang <baolin.wang@...aro.org> wrote:
> >> On 17 November 2015 at 21:34, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> >>> On Mon, Nov 16, 2015 at 9:05 AM, Baolin Wang <baolin.wang@...aro.org> wrote:
> >>>> It dose not work when we want to use the usb-to-serial port based
> >>>> on one usb gadget as a console. Thus this patch adds the console
> >>>> initialization to support this request.
> >>>
> >
> >>>> +#define GS_BUFFER_SIZE         (4096)
> >>> Redundant parens
> >> OK. I'll remove it.
> >>
> >>>> +#define GS_CONSOLE_BUF_SIZE    (2 * GS_BUFFER_SIZE)
> >>>> +
> >>>> +struct gscons_info {
> >>>> +       struct gs_port          *port;
> >>>> +       struct tty_driver       *tty_driver;
> >>>> +       struct work_struct      work;
> >>>> +       int                     buf_tail;
> >>>> +       char                    buf[GS_CONSOLE_BUF_SIZE];
> >>>
> >>> Can't be malloced once?
> >> The 'gscons_info' structure is malloced once.
> >
> > In state of high fragmentation is quite hard to find big memory chunks.
> > I would split it to two allocations, though if maintainers are okay
> > with your code, then I'm also okay.
> >
> 
> Make sense. But I think the major memory of the 'struct gscons_info'
> is for the 'buf' member, so I still think no need to allocate it 2
> times.

It may be worth just reducing GS_BUFFER_SIZE slightly so that the gscons_info
structure itself is less than 8k.
If you can't get 2 adjacent pages then a lot of things will fail.

	David