From: Peter Hurley <peter@hurleysoftware.com>
To: "Sören Brinkmann" <soren.brinkmann@xilinx.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jslaby@suse.com>,
linux-arm-kernel@lists.infradead.org,
Michal Simek <michal.simek@xilinx.com>,
linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in start_tx
Date: Fri, 20 Nov 2015 12:12:29 -0500 [thread overview]
Message-ID: <564F547D.4070808@hurleysoftware.com> (raw)
In-Reply-To: <20151120170525.GW32017@xsjsorenbubuntu>
On 11/20/2015 12:05 PM, Sören Brinkmann wrote:
> On Fri, 2015-11-20 at 07:13AM -0500, Peter Hurley wrote:
>>
>>
>> On 11/19/2015 03:02 PM, Soren Brinkmann wrote:
>>> start_tx must start transmitting characters. Regardless of the state of
>>> the circular buffer, always enable the transmitter hardware.
>>
>> Why?
>>
>> Does cdns_uart_stop_tx() actually stop the transmitter so that
>> data remains in the transmitter?
>
> Fixing up the patch, I looked at this one. It might actually do that.
Ok.
> Without having changed anything. The doc says: "The driver should
> stop transmitting characters as soon as possible.". And the
> implementation is really not draining any FIFO, but just disabling the
> transmitter. I take your question as that this might not be this way?
> Should stop_tx drain the FIFO first?
No.
Most h/w can't actually stop the transmitter (or not without losing
data), so that's why the expectation is only for "as soon as possible".
Stopping sooner is better.
Regards,
Peter Hurley
next prev parent reply other threads:[~2015-11-20 17:12 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-19 20:02 [PATH RESEND v2 00/10] tty: xuartps: Fix lock ups Soren Brinkmann
2015-11-19 20:02 ` [PATH RESEND v2 01/10] tty: xuartps: Beautify read-modify writes Soren Brinkmann
2015-11-19 20:02 ` [PATH RESEND v2 02/10] tty: xuartps: Use spinlock to serialize HW access Soren Brinkmann
2015-11-19 20:02 ` [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in start_tx Soren Brinkmann
2015-11-20 12:13 ` Peter Hurley
2015-11-20 15:28 ` Sören Brinkmann
2015-11-20 16:30 ` Peter Hurley
2015-11-20 16:58 ` Sören Brinkmann
2015-11-20 17:16 ` Peter Hurley
2015-11-20 17:29 ` Sören Brinkmann
2015-11-23 7:05 ` Michal Simek
2015-11-23 20:00 ` Peter Hurley
2015-11-24 7:26 ` Michal Simek
2015-11-20 17:05 ` Sören Brinkmann
2015-11-20 17:12 ` Peter Hurley [this message]
2015-11-19 20:02 ` [PATH RESEND v2 04/10] tty: xuartps: Clear interrupt status register in shutdown Soren Brinkmann
2015-11-19 20:02 ` [PATH RESEND v2 05/10] tty: xuartps: Improve startup function Soren Brinkmann
2015-11-19 20:02 ` [PATH RESEND v2 06/10] tty: xuartps: Keep lock for whole ISR Soren Brinkmann
2015-11-19 20:02 ` [PATH RESEND v2 07/10] tty: xuartps: Acquire port lock for shutdown Soren Brinkmann
2015-11-19 20:02 ` [PATH RESEND v2 08/10] tty: xuartps: Move RX path into helper function Soren Brinkmann
2015-11-19 20:02 ` [PATH RESEND v2 09/10] tty: xuartps: Only handle RX IRQs when RX is enabled Soren Brinkmann
2015-11-19 20:02 ` [PATH RESEND v2 10/10] tty: xuartps: Cleanup: Reformat if-else Soren Brinkmann
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