linux-kernel - Re: [PATCH] tty: serial: msm

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Date:	Thu, 13 Nov 2014 16:59:53 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	frowand.list@...il.com
CC:	Kevin Hilman <khilman@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-serial@...r.kernel.org, Olof Johansson <olof@...om.net>,
	Arnd Bergmann <arnd@...db.de>,
	Tyler Baker <tyler.baker@...aro.org>
Subject: Re: [PATCH] tty: serial: msm_serial: Use DT aliases

On 11/13/2014 04:46 PM, Frank Rowand wrote:
> On 11/13/2014 11:31 AM, Stephen Boyd wrote:
>> Sorry, I'm sort of lost. If there are serial aliases in the dts file,
>> then we should alias all of the serial ports. If there aren't aliases
>> then we're backwards compatible with the dts we have now and we'll do
>> dynamic generation. Putting code into the driver to validate that
>> this is true is not the job of the driver. If anything, it should
>> validated when the dts file is created. If one day we screw up and
>> have a dts file with such a bad configuration we'll have to work
>> around it, but until that day comes I'd rather not think about it. 
> Maybe I did not understand when you said "Perhaps we should use an ida".
> That sentence led me to think the driver should check for misconfiguration.
> The case I was trying to handle was if there was at least one serialN
> alias and at least one UART without an alias.  For example, if there
> are three UARTs (serial_a, serial_b, serial_c, probed in that order)
> and one alias (serial0 = &serial_c;) then the result would be:
>
>    serial_a  line 0 (from msm_uart_next_id)
>    serial_b  line 1 (from msm_uart_next_id)
>    serial_c  line 0 (from the alias)
>
>    Two UARTs probed with line == 0.  This is an error.
>
> Most of the serial drivers don't check for this type of bad configuration.
> Some drivers keep a bit map of which lines have been used.  I'm not sure
> what they do in case of a conflict (I did not read to that level of detail).
>
> I thought you were suggesting the driver check for the bad configuration,
> so I was proposing a somewhat simple way of forcing a boot error for the
> bad configuration.
>
> Since you are not suggesting the driver check for the bad configuration,
> you can ignore my proposal.  I agree that it is ok for the driver to
> expect the board dts to be correct.  The problem should be detected by
> the dts author on first boot as part of normal bring up testing, and
> then corrected.
>

Ah ok. I was just saying we could use an ida instead of an atomic
increment so that this driver works properly with driver
binding/unbinding, otherwise the line number keeps increasing and
quickly goes beyond the static array of ports (which I still don't
understand why we have at all btw).

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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