From: Doug Anderson <dianders@chromium.org>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Ulf Hansson <ulf.hansson@linaro.org>,
Jaehoon Chung <jh80.chung@samsung.com>,
Shawn Lin <shawn.lin@rock-chips.com>,
Adrian Hunter <adrian.hunter@intel.com>,
Stefan Agner <stefan@agner.ch>,
"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
Brian Norris <computersforpeace@gmail.com>,
Dmitry Torokhov <dmitry.torokhov@gmail.com>,
Heiko Stuebner <heiko@sntech.de>,
Jisheng Zhang <jszhang@marvell.com>,
"open list:ARM/Rockchip SoC..."
<linux-rockchip@lists.infradead.org>,
devicetree-spec@vger.kernel.org,
Mark Rutland <mark.rutland@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Venu Byravarasu <vbyravarasu@nvidia.com>,
Lars-Peter Clausen <lars@metafoo.de>,
Jon Hunter <jonathanh@nvidia.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
Pawel Moll <pawel.moll@arm.com>,
Ian Campbell <ijc+devicetree@hellion.org.uk>,
Grant Grundler <grundler@chromium.org>,
Kumar Gala <galak@codeaurora.org>,
"Luca Porzio (lporzio)" <lporzio@micron.com>,
Rob Herring <robh+dt@kernel.org>,
Chaotian Jing <chaotian.jing@mediatek.com>,
Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>,
Sudeep Holla <sudeep.holla@arm.com>,
zhonghui.fu@linux.intel.com, kirill.shutemov@linux.intel.com
Subject: Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering w/ device tree
Date: Fri, 29 Apr 2016 16:01:58 -0700 [thread overview]
Message-ID: <CAD=FV=U5jnJJ3v=nFGFecoKB5KGv1ufC+aKbHx2iCqBTWpDTww@mail.gmail.com> (raw)
In-Reply-To: <20160429224407.GF19428@n2100.arm.linux.org.uk>
Hi,
On Fri, Apr 29, 2016 at 3:44 PM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> My reply would be... why should MMC have special handling that no
> other subsystem has?
No other subsystem?
* i2c allows numbering devices by alias
* rtc allows numbering devices by alias.
* serial allows numbering devices by alias.
* spi allows numbering devices by alias.
* watchdog allows numbering devices by alias.
...at least that's my impression doing a grep for of_alias_get_id(),
which I suggested earlier in this thread but apparently wasn't done.
> Here's another example. Plug in several USB serial adapters. Which
> USB serial /dev/ttyUSB* device corresponds to which adapter? The
> answer is... it depends on the order you plug them in, which could
> well be different from the order in which they are found if the
> machine reboots. That's a very real problem.
USB is, by definition, hotplug and probable and there is no ordering.
For peripherals built-in to a SoC there is a sane ordering. Thus
hotplug peripherals and builtin peripherals shouldn't have the same
requirements.
Quite honestly, it _would_ be quite convenient that if you are on a
SoC and you know it has builtin USB controllers to have the root hubs
numbered in a sane and consistent manner. An area for a future patch,
maybe.
> However, the answer to this problem is not to find some way to bind
> a particular /dev/ttyUSB* node to a particular USB device, but to
> use the solution(s) already provided - iow, /dev/serial/by-id or
> /dev/serial/by-path trees which give a stable view of these devices.
>
> Now, while that allows the appropriate /dev/ttyUSB* device to be
> found, it doesn't solve the "which ttyUSB* entry in the kernel
> message log corresponds with which adapter" (which is the basis
> of your point #1.) That's not solved, and isn't purposely isn't
> solved for any kernel subsystem.
>
> Another example - I have boards here with multiple RTCs... guess
> what happens with those? Yep, same problem. They get dynamic
> /dev/rtc* assignment.
Are you quite certain about that? See above.
> Another example - I have a board with three ethernet devices...
> yep, same problem again, the order depends on the driver probe
> order, and they get dynamically assigned eth* names.
Ethernet is often provided by USB and thus hotplug and probable.
Quite honestly if there was a builtin Ethernet adapter provided on a
SoC (not connected over USB), it would be super handy if it was forced
to be "eth0" (and if there were more than one if they could be ordered
in a way that made sense for that SoC). Dynamic ordering could come
after.
> The list of subsystems that have this property is large, because
> it's all dependent on the device/driver probing order.
Sure. For hotplug, there is no sane device ordering.
For things built in to an SoC, there is sane device ordering. Dynamic
ordering should come after static.
> So, please answer this question: why should _only_ MMC be treated
> as a special case? Please give a _technical_ reason rather than a
> _personal_ reason.
Because technically it makes it easier for people to understand their
system to have a sane ordering for builtin peripherals.
-Doug
next prev parent reply other threads:[~2016-04-29 23:02 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-29 17:32 [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering w/ device tree Douglas Anderson
2016-04-29 17:32 ` [PATCH v2 1/4] Documentation: mmc: Document mmc aliases Douglas Anderson
2016-04-29 17:32 ` [PATCH v2 2/4] mmc: read mmc alias from device tree Douglas Anderson
2016-04-29 17:32 ` [PATCH v2 3/4] mmc: use SD/MMC host ID for block device name ID Douglas Anderson
2016-04-29 17:32 ` [PATCH v2 4/4] ARM: dts: rockchip: Add mmc aliases for rk3288 platform Douglas Anderson
2016-04-29 18:12 ` [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering w/ device tree Rob Herring
2016-04-29 19:31 ` Doug Anderson
2016-04-29 19:50 ` Russell King - ARM Linux
2016-04-29 20:02 ` Doug Anderson
2016-04-29 18:12 ` Russell King - ARM Linux
2016-04-29 19:43 ` Doug Anderson
2016-04-29 19:57 ` Russell King - ARM Linux
2016-04-29 20:04 ` Doug Anderson
2016-04-29 21:13 ` Russell King - ARM Linux
2016-04-29 21:17 ` Doug Anderson
2016-04-29 21:29 ` Russell King - ARM Linux
2016-04-29 21:39 ` Doug Anderson
2016-04-29 21:50 ` Russell King - ARM Linux
2016-04-29 21:56 ` Doug Anderson
2016-04-29 22:16 ` Russell King - ARM Linux
2016-04-29 22:22 ` Doug Anderson
2016-04-29 22:44 ` Russell King - ARM Linux
2016-04-29 23:01 ` Doug Anderson [this message]
2016-04-29 23:58 ` Peter Hurley
[not found] ` <CAD=FV=V_YyfBOSs7BLkyhv=_5HBmf3djUWACbL6d-bwnrueDjA@mail.gmail.com>
2016-04-30 0:31 ` Peter Hurley
2016-04-30 2:29 ` Doug Anderson
2016-04-30 8:38 ` Russell King - ARM Linux
2016-04-30 13:23 ` Rob Herring
2016-04-29 22:42 ` Javier Martinez Canillas
2016-04-30 10:48 ` Russell King - ARM Linux
2016-05-03 19:17 ` Trent Piepho
2016-05-04 7:18 ` Pavel Machek
2016-05-04 12:25 ` Rob Herring
2016-05-04 12:46 ` Pavel Machek
2019-03-05 12:39 ` Måns Rullgård
2019-03-15 21:52 ` Tim Harvey
2019-03-15 23:00 ` Marek Vasut
2019-03-15 23:13 ` Tim Harvey
2019-03-15 23:23 ` Doug Anderson
[not found] ` <yw1xftrn2em9.fsf@mansr.com>
2019-03-16 12:33 ` Marek Vasut
2019-03-16 15:39 ` Russell King - ARM Linux admin
2019-03-17 15:05 ` Stefan Agner
2019-03-17 15:43 ` Russell King - ARM Linux admin
2019-03-17 15:50 ` Marek Vasut
2019-03-17 16:48 ` Måns Rullgård
2019-03-17 16:59 ` Russell King - ARM Linux admin
2019-03-27 17:37 ` Tim Harvey
2019-03-27 20:54 ` Russell King - ARM Linux admin
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