From: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
To: Ezequiel Garcia <ezequiel@collabora.com>
Cc: "Matwey V. Kornilov" <matwey@sai.msu.ru>,
Alan Stern <stern@rowland.harvard.edu>,
Hans de Goede <hdegoede@redhat.com>,
hverkuil@xs4all.nl, mchehab@kernel.org,
Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
rostedt@goodmis.org, mingo@redhat.com, isely@pobox.com,
bhumirks@gmail.com, colin.king@canonical.com,
linux-media@vger.kernel.org,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] media: usb: pwc: Don't use coherent DMA buffers for ISO transfer
Date: Mon, 30 Jul 2018 13:07:02 -0300 [thread overview]
Message-ID: <20180730130702.27664d15@coco.lan> (raw)
In-Reply-To: <eb2b495fe7e8bbeaf3f9e2814be4923583482852.camel@collabora.com>
Em Tue, 17 Jul 2018 17:10:22 -0300
Ezequiel Garcia <ezequiel@collabora.com> escreveu:
> Yeah, and not setting URB_NO_TRANSFER_DMA_MAP makes the USB core
> create DMA mappings and use the streaming API. Which makes more
> sense in hardware without hardware coherency.
>
> The only thing that bothers me with this patch is that it's not
> really something specific to this driver. If this fix is valid
> for pwc, then it's valid for all the drivers allocating coherent
> memory.
We're actually doing this change on other drivers:
https://git.linuxtv.org/media_tree.git/commit/?id=d571b592c6206
I suspect that the reason why all USB media drivers were using
URB_NO_TRANSFER_DMA_MAP is just because the first media USB driver
upstream used it.
On that time, I remember I tried once to not use this flag, but there
was something that broke (perhaps I just didn't know enough about the
USB layer - or perhaps some fixes happened at USB core - allowing it
to be used with ISOC transfers).
Anyway, nowadays, I fail to see a reason why not let the USB core
do the DMA maps. On my tests after this patch, at the boards I tested
(arm and x86), I was unable to see any regressions.
Thanks,
Mauro
next prev parent reply other threads:[~2018-07-30 17:43 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-17 14:36 [PATCH 1/2] Add TRACE_EVENTs in pwc_isoc_handler() Matwey V. Kornilov
2018-06-17 14:36 ` [PATCH 2/2] media: usb: pwc: Don't use coherent DMA buffers for ISO transfer Matwey V. Kornilov
2018-06-18 5:11 ` Ezequiel Garcia
2018-06-18 7:10 ` Matwey V. Kornilov
2018-07-17 20:10 ` Ezequiel Garcia
2018-07-17 20:51 ` Alan Stern
2018-07-20 10:55 ` Tomasz Figa
2018-07-20 11:22 ` Matwey V. Kornilov
2018-07-20 11:33 ` Tomasz Figa
2018-07-20 11:57 ` Matwey V. Kornilov
2018-07-23 17:04 ` Matwey V. Kornilov
2018-07-23 18:57 ` Alan Stern
2018-07-24 18:56 ` Matwey V. Kornilov
2018-07-24 20:55 ` Alan Stern
2018-07-25 13:46 ` Matwey V. Kornilov
2018-07-30 4:14 ` Tomasz Figa
2018-08-04 8:05 ` Matwey V. Kornilov
2018-07-30 15:35 ` Laurent Pinchart
2018-08-04 8:00 ` Matwey V. Kornilov
2018-08-04 14:46 ` Alan Stern
2018-08-05 7:49 ` Christoph Hellwig
2018-08-05 8:33 ` Matwey V. Kornilov
2018-08-05 8:41 ` Christoph Hellwig
2018-08-08 22:32 ` Laurent Pinchart
2018-08-09 2:36 ` Tomasz Figa
2018-08-09 10:28 ` Laurent Pinchart
2018-07-30 15:13 ` Laurent Pinchart
2018-07-18 12:10 ` Matwey V. Kornilov
2018-07-19 23:36 ` Ezequiel Garcia
2018-07-20 9:35 ` Matwey V. Kornilov
2018-07-30 15:42 ` Laurent Pinchart
2018-07-30 16:07 ` Mauro Carvalho Chehab [this message]
2018-07-31 6:06 ` Tomasz Figa
2018-06-18 18:58 ` [PATCH 1/2] Add TRACE_EVENTs in pwc_isoc_handler() Steven Rostedt
2018-06-19 16:23 ` Matwey V. Kornilov
2018-06-19 16:33 ` Steven Rostedt
2018-06-20 8:05 ` Matwey V. Kornilov
2018-06-20 13:09 ` Steven Rostedt
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