From: Robert Jarzmik <robert.jarzmik@free.fr>
To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Mark Brown <broonie@kernel.org>,
linux-spi@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
Daniel Mack <daniel@zonque.org>,
Haojian Zhuang <haojian.zhuang@gmail.com>,
linux-kernel@vger.kernel.org,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Mika Westerberg <mika.westerberg@linux.intel.com>,
Jarkko Nikula <jarkko.nikula@linux.intel.com>,
Sascha Weisenberger <sascha.weisenberger@siemens.com>
Subject: Re: [PATCH v2 2/3] spi: pxa2xx: Prepare for edge-triggered interrupts
Date: Tue, 17 Jan 2017 08:54:56 +0100 [thread overview]
Message-ID: <87ziiqdstr.fsf@belgarion.home> (raw)
In-Reply-To: <7b15a0910a3ad861fd32161c72559bafa7b71e29.1484592296.git.jan.kiszka@siemens.com> (Jan Kiszka's message of "Mon, 16 Jan 2017 19:44:55 +0100")
Jan Kiszka <jan.kiszka@siemens.com> writes:
> When using the a device with edge-triggered interrupts, such as MSIs,
> the interrupt handler has to ensure that there is a point in time during
> its execution where all interrupts sources are silent so that a new
> event can trigger a new interrupt again.
>
> This is achieved here by looping over SSSR evaluation. We need to take
> into account that SSCR1 may be changed by the transfer handler, thus we
> need to redo the mask calculation, at least regarding the volatile
> interrupt enable bit (TIE).
>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Hi Jan,
> + while (1) {
This bit worries me a bit, as this can be either :
- hogging the SoC's CPU, endlessly running
- or even worse, blocking the CPU for ever
The question behind is, should this be done in a top-half, or moved to a irq
thread ?
> + /* Ignore possible writes if we don't need to write */
> + if (!(sccr1_reg & SSCR1_TIE))
> + mask &= ~SSSR_TFS;
>
> - if (!drv_data->master->cur_msg) {
> - handle_bad_msg(drv_data);
> - /* Never fail */
> - return IRQ_HANDLED;
> - }
> + if (!(status & mask))
> + return ret;
> +
> + if (!drv_data->master->cur_msg) {
> + handle_bad_msg(drv_data);
> + /* Never fail */
> + return IRQ_HANDLED;
> + }
> +
> + ret |= drv_data->transfer_handler(drv_data);
Mmm that looks weird to me, oring a irqreturn.
Imagine that on first iteration the handler returns IRQ_NONE, and on second
IRQ_HANDLED. This makes ret IRQ_HANDLED. Yet after the first iteration the
handler should have exited, especially if the interrupt is shared with another
driver.
Another thing which is along what Andy already said : it would be better
practice to have this loop in the form :
do {
...
} while (exit_condition_not_met);
Just for maintainability, it's better, and it concentrates the test on the
"exit_condition_not_met" in one place, which will enable us to review better the
algorithm.
Cheers.
--
Robert
next prev parent reply other threads:[~2017-01-17 7:56 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-16 18:44 [PATCH v2 0/3] spi: pca2xx: Prepare for and enable MSI support Jan Kiszka
2017-01-16 18:44 ` [PATCH v2 1/3] spi: pxa2xx: Factor out handle_bad_msg Jan Kiszka
2017-01-17 11:18 ` Jarkko Nikula
2017-01-17 18:46 ` Applied "spi: pxa2xx: Factor out handle_bad_msg" to the spi tree Mark Brown
2017-01-16 18:44 ` [PATCH v2 2/3] spi: pxa2xx: Prepare for edge-triggered interrupts Jan Kiszka
2017-01-16 19:07 ` Andy Shevchenko
2017-01-16 19:46 ` Jan Kiszka
2017-01-17 18:52 ` Jan Kiszka
2017-01-17 7:54 ` Robert Jarzmik [this message]
2017-01-17 8:05 ` Jan Kiszka
2017-01-18 8:21 ` Robert Jarzmik
2017-01-18 9:33 ` Jan Kiszka
2017-01-18 12:46 ` Mark Brown
2017-01-19 15:34 ` Jan Kiszka
2017-01-19 19:37 ` [PATCH v3 " Jan Kiszka
2017-01-19 19:57 ` Mark Brown
2017-01-19 20:04 ` Andy Shevchenko
2017-01-20 12:21 ` Mark Brown
2017-01-20 15:29 ` Jan Kiszka
2017-01-20 16:14 ` Mark Brown
2017-01-20 7:42 ` Robert Jarzmik
2017-01-24 18:39 ` Applied "spi: pxa2xx: Prepare for edge-triggered interrupts" to the spi tree Mark Brown
2017-01-17 7:58 ` [PATCH v2 2/3] spi: pxa2xx: Prepare for edge-triggered interrupts Robert Jarzmik
2017-01-17 8:10 ` Jan Kiszka
2017-01-17 13:11 ` Jarkko Nikula
2017-01-17 14:43 ` Jan Kiszka
2017-01-16 18:44 ` [PATCH v2 3/3] spi: pca2xx-pci: Allow MSI Jan Kiszka
2017-01-16 19:08 ` Andy Shevchenko
2017-01-17 11:18 ` Jarkko Nikula
2017-01-24 18:39 ` Applied "spi: pca2xx-pci: Allow MSI" to the spi tree Mark Brown
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