Re: [PATCH v4] usb: musb: Enable DMA mode1 RX for USB-Mass-Storage

From: Jassi Brar <jassisinghbrar@gmail.com>
To: "Pandita, Vikram" <vikram.pandita@ti.com>
Cc: balbi@ti.com, linux-usb@vger.kernel.org, gadiyar@ti.com,
	linux-omap@vger.kernel.org, Moiz Sonasath <m-sonasath@ti.com>
Subject: Re: [PATCH v4] usb: musb: Enable DMA mode1 RX for USB-Mass-Storage
Date: Wed, 20 Jul 2011 11:23:48 +0530	[thread overview]
Message-ID: <CABb+yY0QsO-rh6Q9nffmPp=4sYi=6Csor1VPdhLvAXd5LJVeRg@mail.gmail.com> (raw)
In-Reply-To: <CAFm5wm3zZyMgScH6OqmVVW32mLUJ6OGcmDy+Wz9Gc7EBjsswJQ@mail.gmail.com>

On Wed, Jul 20, 2011 at 11:15 AM, Pandita, Vikram <vikram.pandita@ti.com> wrote:
> On Tue, Jul 19, 2011 at 10:34 PM, Jassi Brar <jassisinghbrar@gmail.com> wrote:
>>
>> On Wed, Jul 20, 2011 at 10:41 AM, Vikram Pandita <vikram.pandita@ti.com> wrote:
>> > From: Anand Gadiyar <gadiyar@ti.com>
>> >
>> > This patch enables the DMA mode1 RX support.
>> > This feature is enabled based on the short_not_ok flag passed from
>> > gadget drivers.
>> >
>> > This will result in a thruput performance gain of around
>> > 40% for USB mass-storage/mtp use cases.
>> >
>> > Signed-off-by: Anand Gadiyar <gadiyar@ti.com>
>> > Signed-off-by: Moiz Sonasath <m-sonasath@ti.com>
>> > Signed-off-by: Vikram Pandita <vikram.pandita@ti.com>
>> > Tested-by: Vikram Pandita <vikram.pandita@ti.com>
>> > ---
>> > v1 - initial push
>> > v2 - fixed whitespace issues as per Sergei Shtylyov<sshtylyov@mvista.com> comments
>> > v3 - restor authorship to Anand Gadiyar <gadiyar@ti.com>
>> > v4 - adding my signed-off as per Kevin Hilman <khilman@ti.com>
>> >
>> >  drivers/usb/musb/musb_gadget.c |   68 ++++++++++++++++++++++++---------------
>> >  1 files changed, 42 insertions(+), 26 deletions(-)
>>
>> > @@ -683,6 +684,18 @@ static void rxstate(struct musb *musb, struct musb_request *req)
>> >
>> >        if (csr & MUSB_RXCSR_RXPKTRDY) {
>> >                len = musb_readw(epio, MUSB_RXCOUNT);
>> > +
>> > +               /*
>> > +                * Enable Mode 1 for RX transfers only for mass-storage
>> > +                * use-case, based on short_not_ok flag which is set only
>> > +                * from file_storage and f_mass_storage drivers
>> > +                */
>> > +
>> > +               if (request->short_not_ok && len == musb_ep->packet_sz)
>> > +                       use_mode_1 = 1;
>> > +               else
>> > +                       use_mode_1 = 0;
>> > +
>> There is nothing UMS class specific in this patch...
>> (request->short_not_ok && len == musb_ep->packet_sz) may not be the
>> signature of, and only of, Mass Storage Functions. So maybe removing
>> the UMS mention from
>> comment and change-log is a good idea.
>
> Have you grepped the code in drivers/usb/gadget/*.*
> only UMS sets this flag today and hence the use of this flag.
>
> As i understand, on UMS, CSW/data/CBW  - the data part size is a known
> size and to be safe that mode=1 dma is not stuck up,
> the mode is enabled only for the gadget driver that sets short_not_ok
> flag - and that today happens to be only UMS.

This *today happens to be only UMS* is my exact point here.
Can you guarantee no other function driver will ever expect only
full packet xfers and treat short as errors ?

>> You might want to add is-ep-type-bulk-out check to the condition
>> though, so that it doesn't affect
>> cases that you didn't verify.
>
> TX path (IN host), already uses the mode=1 DMA and hence the comment
> is not valid.
> This patch just also enables mode=1 on RX path.
Well, then no need for the ep-type check.
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