Re: [PATCH] Force set console baudrate

[Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>]

On Jul 10, 2013, at 4:09 AM, Alexey Galakhov <agalakhov@gmail.com> wrote:

> Hi,
> 
> On 07/10/2013 12:57 AM, Jean-Christophe PLAGNIOL-VILLARD wrote:
>> 
>> On Jul 10, 2013, at 1:43 AM, Sascha Hauer <s.hauer@pengutronix.de> wrote:
>> 
>>> On Tue, Jul 09, 2013 at 09:22:10PM +0600, Alexey Galakhov wrote:
>>>> Most serial drivers require setbrg() to be called at least once. Call them
>>>> just after the device has been added.
>>>> 
>>>> Signed-off-by: Alexey Galakhov <agalakhov@gmail.com>
>> 
>> This is wrong if you do this at boot which means you force the same baudrate
>> on all the console
> 
> This does NOT force the same baudrate. It just ensures that the default
> baudrate will not be ignored. There is no problem setting another
> baudrate later if desired by using "baudrate" parameter from the shell
> or something.

This does force the same baud rate on ALL console device at register time => wrong

> 
>> We must do this only is enable by default of via shell
> 
> There is "chicken and egg" problem. barebox_banner() requires valid
> baudrate setting and may deadlock without it. (It WILL deadlock on most
> serial drivers and really deadlocks on S3C one).

so do is at enable time not register time

> 
>> and some console may not need the setbrg call back (keyboard or fbdev as example)
> 
> If the device does not have setbrg() function defined, nothing will be
> called. This all is under if (newcdev->setbrg) anyway.

this will result is a call of a NULL pointer -> crash
> 
>> Also if we want to use a rs232 for controlling a mcu the baud rate may not be the
>> CONFIG_BAUDRATE
> 
> No problem, there is a parameter. Just set it before activating the device.
> 
>> so force it at register is wrong
> 
> Not setting it is much worse. It will result in deadlock at the first
> attempt to write to the console since setbrg() will not be called at all.
> 
> The idea is, if there IS a function to set a baudrate and there IS a
> default setting, the baudrate SHOULD be initialized before doing
> anything else.  Changing the baudrate on an inactive device multiple
> times is (or at least should be) harmless. Trying to activate the device
> with baudrate unset is not.
> 

If the console is not enable there no need to do anything
you need to set the baud rate ONLY if the device is enable

> Regards,
> Alex


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