From: "Shenhar, Talel" <talel@amazon.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Mark Rutland <mark.rutland@arm.com>,
mjourdan@baylibre.com, Catalin Marinas <catalin.marinas@arm.com>,
Linus Walleij <linus.walleij@linaro.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
jonnyc@amazon.com,
Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
ronenk@amazon.com, Will Deacon <will@kernel.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
DTML <devicetree@vger.kernel.org>,
Maxime Ripard <mripard@kernel.org>,
Rob Herring <robh+dt@kernel.org>,
Santosh Shilimkar <ssantosh@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
hanochu@amazon.com,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
barakw@amazon.com, hhhawa@amazon.com,
gregkh <gregkh@linuxfoundation.org>,
paul.kocialkowski@bootlin.com,
Patrick Venture <venture@google.com>,
Olof Johansson <olof@lixom.net>,
David Miller <davem@davemloft.net>,
David Woodhouse <dwmw@amazon.co.uk>
Subject: Re: [PATCH 2/3] soc: amazon: al-pos: Introduce Amazon's Annapurna Labs POS driver
Date: Tue, 10 Sep 2019 09:21:01 +0300 [thread overview]
Message-ID: <b50ba032-51f7-3cd1-a302-30146560f636@amazon.com> (raw)
In-Reply-To: <CAK8P3a1fbK-qoK+K1ZsWsU3rkxxZgZGaK8ywFAcM4va1GRn_FQ@mail.gmail.com>
On 9/9/2019 6:16 PM, Arnd Bergmann wrote:
> On Mon, Sep 9, 2019 at 4:11 PM Shenhar, Talel <talel@amazon.com> wrote:
>> On 9/9/2019 4:41 PM, Arnd Bergmann wrote:
>>
>> In current implementation of v1, I am not doing any read barrier, Hence,
>> using the non-relaxed will add unneeded memory barrier.
>>
>> I have no strong objection moving to the non-relaxed version and have an
>> unneeded memory barrier, as this path is not "hot" one.
> Ok, then please add it.
ok, shall be part of v2
>
>> Beside of avoiding the unneeded memory barrier, I would be happy to keep
>> common behavior for our drivers:
>>
>> e.g.
>>
>> https://github.com/torvalds/linux/blob/master/drivers/irqchip/irq-al-fic.c#L49
>>
>>
>> So what do you think we should go with? relaxed or non-relaxed?
> The al_fic_set_trigger() function is clearly a slow-path and should use the
> non-relaxed functions. In case of al_fic_irq_handler(), the extra barrier
> might introduce a measurable overhead, but at the same time I'm
> not sure if that one is correct without the barrier:
>
> If you have an MSI-type interrupt for notifying a device driver of
> a DMA completion, there might not be any other barrier between
> the arrival of the MSI message and the CPU accessing the data.
> Depending on how strict the hardware implements MSI and how
> the IRQ is chained, this could lead to data corruption.
>
> If the interrupt is only used for level or edge triggered interrupts,
> this is ok since you already need another register read in
> the driver before it can safely access a DMA buffer.
>
> In either case, if you can prove that it's safe to use the relaxed
> version here and you think that it may help, it would be good to
> add a comment explaining the reasoning.
Decided to go with the non-relaxed version as this is not hot path and
likely be more clear to the common reader to have non relaxed version.
>
> Arnd
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next prev parent reply other threads:[~2019-09-10 6:22 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-09 9:10 [PATCH 0/3] Amazon's Annapurna Labs POS Driver Talel Shenhar
2019-09-09 9:10 ` [PATCH 1/3] dt-bindings: soc: al-pos: Amazon's Annapurna Labs POS Talel Shenhar
2019-09-09 9:10 ` [PATCH 2/3] soc: amazon: al-pos: Introduce Amazon's Annapurna Labs POS driver Talel Shenhar
2019-09-09 9:44 ` Arnd Bergmann
2019-09-09 11:12 ` Shenhar, Talel
2019-09-09 13:41 ` Arnd Bergmann
2019-09-09 14:11 ` Shenhar, Talel
2019-09-09 15:16 ` Arnd Bergmann
2019-09-10 6:21 ` Shenhar, Talel [this message]
2019-09-09 11:51 ` kbuild test robot
2019-09-09 9:10 ` [PATCH 3/3] arm64: alpine: select AL_POS Talel Shenhar
2019-09-09 9:40 ` Arnd Bergmann
2019-09-09 10:16 ` Shenhar, Talel
2019-09-09 13:45 ` Arnd Bergmann
2019-09-09 13:58 ` Shenhar, Talel
2019-09-09 15:08 ` Arnd Bergmann
2019-09-10 6:17 ` Shenhar, Talel
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