From: Martin Sperl <kernel@martin.sperl.org>
To: "Noralf Trønnes" <noralf@tronnes.org>,
wsa@the-dreams.de, swarren@wwwdotorg.org, eric@anholt.net
Cc: linux-rpi-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-i2c@vger.kernel.org
Subject: Re: [PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes
Date: Tue, 20 Sep 2016 08:46:58 +0200 [thread overview]
Message-ID: <e473206c-7f9c-7b7d-d75d-7879425fc2f9@martin.sperl.org> (raw)
In-Reply-To: <1474298777-5858-1-git-send-email-noralf@tronnes.org>
On 19.09.2016 17:26, Noralf Trønnes wrote:
> Writing messages larger than the FIFO size results in a hang, rendering
> the machine unusable. This is because the RXD status flag is set on the
> first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
> from the buffer. The controller continues to trigger interrupts waiting
> for the missing bytes, but bcm2835_fill_txfifo() has none to give.
I remember having seen similar interrupt issues with the SPI HW-block.
> In this situation wait_for_completion_timeout() apparently is unable to
> stop the madness.
That is because it is a level irq that immediately triggers another
interrupt giving
no CPU no time to do other (threaded) OS activity - this might be slightly
different for multi-core machines...
> The BCM2835 ARM Peripherals datasheet has this to say about the flags:
> TXD: is set when the FIFO has space for at least one byte of data.
> RXD: is set when the FIFO contains at least one byte of data.
> TXW: is set during a write transfer and the FIFO is less than full.
> RXR: is set during a read transfer and the FIFO is or more full.
>
> Implementing the logic from the downstream i2c-bcm2708 driver solved
> the hang problem.
>
> Signed-off-by: Noralf Trønnes<noralf@tronnes.org>
Reviewed-by: Martin Sperl <kernel@martin.sperl.org>
prev parent reply other threads:[~2016-09-20 7:46 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-19 15:26 [PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes Noralf Trønnes
2016-09-19 15:26 ` [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer Noralf Trønnes
2016-09-20 7:19 ` Martin Sperl
2016-09-20 8:41 ` Noralf Trønnes
2016-09-20 10:15 ` Martin Sperl
2016-09-20 10:56 ` Noralf Trønnes
2016-09-20 11:29 ` kernel
2016-09-21 13:45 ` Noralf Trønnes
2016-09-19 15:26 ` [PATCH 3/3] i2c: bcm2835: Use ratelimited logging on transfer errors Noralf Trønnes
2016-09-19 16:51 ` [PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes Eric Anholt
2016-09-19 17:36 ` Noralf Trønnes
2016-09-20 6:46 ` Martin Sperl [this message]
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