From: Wolfram Sang <wsa@the-dreams.de>
To: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>,
linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] i2c: uniphier-f: fix occasional timeout error
Date: Sun, 28 Oct 2018 22:08:00 +0000 [thread overview]
Message-ID: <20181028220759.GC1882@kunai> (raw)
In-Reply-To: <1539658909-26691-3-git-send-email-yamada.masahiro@socionext.com>
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On Tue, Oct 16, 2018 at 12:01:48PM +0900, Masahiro Yamada wrote:
> Currently, a timeout error could happen at a repeated START condition.
>
> For a (non-repeated) START condition, the controller starts sending
> data when the UNIPHIER_FI2C_CR_STA bit is set. However, for a repeated
> START condition, the hardware starts running when the slave address is
> written to the TX FIFO - the write to the UNIPHIER_FI2C_CR register is
> actually unneeded.
>
> Because the hardware is already running before the IRQ is enabled for
> a repeated START, the driver may miss the IRQ event. In most cases,
> this problem does not show up since modern CPUs are much faster than
> the I2C transfer. However, it is still possible that a context switch
> happens after the controller starts, but before the IRQ register is
> set up.
>
> To fix this,
>
> - Do not write UNIPHIER_FI2C_CR for repeated START conditions.
>
> - Enable IRQ *before* writing the slave address to the TX FIFO.
>
> - Disable IRQ for the current CPU while queuing up the TX FIFO;
> If the CPU is interrupted by some task, the interrupt handler
> might be invoked due to the empty TX FIFO before completing the
> setup.
>
> Fixes: 6a62974b667f ("i2c: uniphier_f: add UniPhier FIFO-builtin I2C driver")
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Applied to for-next, thanks!
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next prev parent reply other threads:[~2018-10-28 22:08 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-16 3:01 [PATCH 0/3] i2c: uniphier-f: fix concurrency issues and race conditions Masahiro Yamada
2018-10-16 3:01 ` [PATCH 1/3] i2c: uniphier-f: make driver robust against concurrency Masahiro Yamada
2018-10-28 22:07 ` Wolfram Sang
2018-10-16 3:01 ` [PATCH 2/3] i2c: uniphier-f: fix occasional timeout error Masahiro Yamada
2018-10-28 22:08 ` Wolfram Sang [this message]
2018-10-16 3:01 ` [PATCH 3/3] i2c: uniphier-f: fix race condition when IRQ is cleared Masahiro Yamada
2018-10-28 22:08 ` Wolfram Sang
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