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From: Arnd Bergmann <arnd@arndb.de>
To: Alex Elder <elder@linaro.org>
Cc: David Miller <davem@davemloft.net>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	Networking <netdev@vger.kernel.org>,
	DTML <devicetree@vger.kernel.org>,
	linux-arm-msm@vger.kernel.org, linux-soc@vger.kernel.org,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	syadagir@codeaurora.org, mjavid@codeaurora.org,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>
Subject: Re: [RFC PATCH 10/12] soc: qcom: ipa: data path
Date: Thu, 15 Nov 2018 06:48:36 -0800
Message-ID: <CAK8P3a3inEwKtfNhD4eT7m2t5eVLMcR5HJWR6-kzO__6F=U_tw@mail.gmail.com> (raw)
In-Reply-To: <a1517ea0-b651-f24e-4890-8ceb6e2b14c6@linaro.org>

On Wed, Nov 14, 2018 at 7:31 PM Alex Elder <elder@linaro.org> wrote:
>
> On 11/7/18 8:55 AM, Arnd Bergmann wrote:
> > On Wed, Nov 7, 2018 at 1:33 AM Alex Elder <elder@linaro.org> wrote:
> >>
> >> This patch contains "ipa_dp.c", which includes the bulk of the data
> >> path code.  There is an overview in the code of how things operate,
> >> but there are already plans to rework this portion of the driver.
> >>
> >> In particular:
> >>   - Interrupt handling will be replaced with a threaded interrupt
> >>     handler.  Currently handling occurs in a combination of
> >>     interrupt and workqueue context, and this requires locking
> >>     and atomic operations for proper synchronization.
> >
> > You probably don't want to use just a threaded IRQ handler to
> > start the poll function, that would still require an extra indirection.
>
> That's a really good point.  However I think that the path I'll
> take to *getting* to scheduling the poll in interrupt context
> will use a threaded interrupt handler.  I'm hoping that will
> allow me to simplify the code in steps.
>
> The main reason for this split between working in interrupt
> context when possible, but pushing to a workqueue when not, is
> to allow IPA clock(s) to be turned off.  Enabling the clocks
> is a blocking operation, so can't' be done in the top half
> interrupt handler.  The thought was it would be best to work
> in interrupt context--if the clock was already active--but
> to defer to a workqueue to turn the clock on if necessary.
>
> The result requires locking and duplication of code that I
> find to be pretty confusing--and hard to reason about.  I
> have been planning to re-do things to be better suited to
> NAPI, and knowing that, I haven't given the data path as
> much attention as some of the rest.

Right, that sounds like a good plan: start making it use a
threaded IRQ handler first to clean up the code, and then
think about optimizing the NAPI wakeup once that works
reliably.

I think what you can do here eventually is to have
a combined threaded/non-threaded IRQ handler, where
the threaded handler can do everything it needs to do,
and the non-threaded handler does only one thing:
if all conditions are met for entering the NAPI handler
(waiting for rx/tx IRQ, clocks enabled, ...) we call
napi_schedule(), otherwise defer to the threaded handler.

       Arnd

  reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-07  0:32 [RFC PATCH 00/12] net: introduce Qualcomm IPA driver Alex Elder
2018-11-07  0:32 ` [RFC PATCH 01/12] dt-bindings: soc: qcom: add IPA bindings Alex Elder
2018-11-07 11:50   ` Arnd Bergmann
2018-11-09 22:38     ` Alex Elder
2018-11-07 14:59   ` Rob Herring
2018-11-09 22:38     ` Alex Elder
2018-11-11  1:40       ` Rob Herring
2018-11-13 16:28     ` Alex Elder
2018-11-07  0:32 ` [RFC PATCH 02/12] soc: qcom: ipa: DMA helpers Alex Elder
2018-11-07 12:17   ` Arnd Bergmann
2018-11-13 16:33     ` Alex Elder
2018-11-07  0:32 ` [RFC PATCH 03/12] soc: qcom: ipa: generic software interface Alex Elder
2018-11-07  0:32 ` [RFC PATCH 04/12] soc: qcom: ipa: immediate commands Alex Elder
2018-11-07 14:36   ` Arnd Bergmann
2018-11-13 16:58     ` Alex Elder
2018-11-07  0:32 ` [RFC PATCH 05/12] soc: qcom: ipa: IPA interrupts and the microcontroller Alex Elder
2018-11-07  0:32 ` [RFC PATCH 06/12] soc: qcom: ipa: QMI modem communication Alex Elder
2018-11-07  0:32 ` [RFC PATCH 07/12] soc: qcom: ipa: IPA register abstraction Alex Elder
2018-11-07 15:00   ` Arnd Bergmann
2018-11-15  2:48     ` Alex Elder
2018-11-15 14:42       ` Arnd Bergmann
2018-11-07  0:32 ` [RFC PATCH 08/12] soc: qcom: ipa: utility functions Alex Elder
2018-11-07  0:32 ` [RFC PATCH 09/12] soc: qcom: ipa: main IPA source file Alex Elder
2018-11-07 14:08   ` Arnd Bergmann
2018-11-15  3:11     ` Alex Elder
2018-11-07  0:32 ` [RFC PATCH 10/12] soc: qcom: ipa: data path Alex Elder
2018-11-07 14:55   ` Arnd Bergmann
2018-11-15  3:31     ` Alex Elder
2018-11-15 14:48       ` Arnd Bergmann [this message]
2018-11-07  0:32 ` [RFC PATCH 11/12] soc: qcom: ipa: IPA rmnet interface Alex Elder
2018-11-07 13:30   ` Arnd Bergmann
2018-11-07 15:26   ` Dan Williams
2018-11-07  0:32 ` [RFC PATCH 12/12] soc: qcom: ipa: build and "ipa_i.h" Alex Elder
2018-11-07  0:40   ` Randy Dunlap
2018-11-08 16:22     ` Alex Elder
2018-11-07 12:34   ` Arnd Bergmann
2018-11-07 15:46 ` [RFC PATCH 00/12] net: introduce Qualcomm IPA driver Arnd Bergmann

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