linux-kernel - Re: [PATCH v3 1/1] serial: imx - Add dma buffer confugration via sysfs

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Date:   Fri, 9 Nov 2018 09:02:57 -0800
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Fabien Lahoudere <fabien.lahoudere@...labora.com>
Cc:     linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH v3 1/1] serial: imx - Add dma buffer confugration via
 sysfs

On Wed, Oct 17, 2018 at 10:20:25AM +0200, Fabien Lahoudere wrote:
> Hi Greg,
> 
> On Mon, 2018-10-15 at 16:01 +0200, Greg KH wrote:
> > On Thu, Oct 11, 2018 at 11:25:03AM +0200, Fabien Lahoudere wrote:
> > > In order to optimize serial communication on imx53 and imx6, we may
> > > need to tweak DMA period and buffer length per period.
> > 
> > Why can you not just automatically determine this information?  What is
> > userspace going to know that the kernel can not just learn now?
> > 
> > Having tunables is nice, but it is even better to not need them at all.
> 
> I agree that it is better to let the kernel do the configuration.

Great!

> However in our case we use several serial communication for different device
> and one of them need to tweak that configuration to get small data with a better
> period. However having this parameter for all serial port implies a bigger number
> of interrupts for others too.

Why can you not dynamically figure this out?  How are you figuring it
out "by hand" today in userspace?

thanks,

greg k-h