From: peter@hurleysoftware•com (Peter Hurley)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v4 2/2] serial: mxs-auart: keep the AUART unit in reset state when not in use
Date: Fri, 07 Aug 2015 11:30:27 -0400 [thread overview]
Message-ID: <55C4CF13.90206@hurleysoftware.com> (raw)
In-Reply-To: <1438944424-9053-2-git-send-email-jbe@pengutronix.de>
On 08/07/2015 06:47 AM, Juergen Borleis wrote:
> Whenever the UART device driver gets closed from userland, the driver
> disables the UART unit and then stops the clocks to save power.
>
> The bit which disabled the UART unit is described as:
>
> "UART Enable. If this bit is set to 1, the UART is enabled. Data
> transmission and reception occurs for the UART signals. When the
> UART is disabled in the middle of transmission or reception, it
> completes the current character before stopping."
>
> The important part is the "it completes the current character". Whenever
> a reception is ongoing when the UART gets disabled (including the clock
> off) the statemachine freezes and "remembers" this state on the next
> open() when re-enabling the unit's clock.
>
> In this case we end up receiving an additional bogus character
> immediately.
>
> The solution in this change is to switch the AUART unit into its reset
> state on close() and only release it from its reset state on the next
> open().
>
> Note: when the unit is also used as system console it is always 'in use',
> so we cannot reset it on close().
The code is still a bit ackward but looks functional, so
Reviewed-by: Peter Hurley <peter@hurleysoftware•com>
PS - This mxs driver has the same problem as the i.MX driver.
The irq request and hardware init should be done in startup().
prev parent reply other threads:[~2015-08-07 15:30 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-07 10:47 [PATCH v4 1/2] serial: mxs-auart: use a function name to reflect what it really does Juergen Borleis
2015-08-07 10:47 ` [PATCH v4 2/2] serial: mxs-auart: keep the AUART unit in reset state when not in use Juergen Borleis
2015-08-07 15:30 ` Peter Hurley [this message]
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