linux-kernel - Re: [Patch] Increase USBFS Bulk Transfer size

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Message-ID: <CA+O4pCL+yLkzCXwMvJE95rTLeYeaf_FHq8YS48OYDZa4YiHnoQ@mail.gmail.com>
Date:	Fri, 14 Oct 2011 05:48:19 +0200
From:	Markus Rechberger <mrechberger@...il.com>
To:	James Courtier-Dutton <james.dutton@...il.com>
Cc:	USB list <linux-usb@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, Greg KH <gregkh@...e.de>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [Patch] Increase USBFS Bulk Transfer size

On Fri, Oct 14, 2011 at 5:42 AM, Markus Rechberger
<mrechberger@...il.com> wrote:
> On Fri, Oct 14, 2011 at 4:47 AM, Markus Rechberger
> <mrechberger@...il.com> wrote:
>> On Fri, Oct 14, 2011 at 12:19 AM, James Courtier-Dutton
>> <james.dutton@...il.com> wrote:
>>> Why don't you try a bulk size of 12032 instead of 24064 and not try 12288 as
>>> you appear to be doing in the logs. Post the logs for that.
>>
>> I tried that earlier already of course it fails. If I could pick a
>> smaller transfer size I would be happy since
>> the device would work with all 2.6.x kernels out of the box and I
>> wouldn't have to waste my time with it.
>> Unfortunately it requires the 24064 bytes.
>> The more flexible device A which is mentioned here confirms that there
>> can be some impact on the
>> bulk transfer size.
>> However to learn about this it's needed to look at the bottom line of
>> USB on the physical layer.
>>
>> And I disagree with Alan Cox it's not about being a crappy device or
>> not, it's more like about something
>> that is not well understood here. Most people are familiar with
>> Software only here and not with the physical
>> USB bottom Layer, otherwise the fact that the devices can have an
>> impact on this wouldn't be such a surprise.
>>
>
> however to not say that I'm unwilling to do that and that is the
> reason for not accepting this patch
> http://www.sundtek.de/support/notworking2.log
>
> even if the value is exposed to sysfs, it still requires the static
> value in the kernel. The current value
> used in the patch is based on what is in the HW specs of device A
> which has the flexible bulk transfer setting.
> The inflexible device which uses 24064 bytes works with all other
> Operating systems by using that value
> and gives exactly the same results with other transfer sizes than that.
>

I didn't check this before the half of it is of course not a multiple
of 512 so the
logfile only shows up 11776 of course.

24064 is the smallest common multiple of 188 and 512.

BR,
Markus
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