linux-kernel - Re: [PATCH 0/3] tty: serial: 8250

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Message-ID: <20170118170726.GE7403@atomide.com>
Date:   Wed, 18 Jan 2017 09:07:26 -0800
From:   Tony Lindgren <tony@...mide.com>
To:     Vignesh R <vigneshr@...com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Peter Hurley <peter@...leysoftware.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: Re: [PATCH 0/3] tty: serial: 8250_omap: Enable DMA support

* Vignesh R <vigneshr@...com> [170118 04:04]:
> 
> 
> On Wednesday 18 January 2017 04:55 AM, Tony Lindgren wrote:
> > * Vignesh R <vigneshr@...com> [170117 02:06]:
> >>
> >>
> >> On Tuesday 17 January 2017 11:36 AM, Vignesh R wrote:
> >>>
> >>>
> >>> On Friday 13 January 2017 11:50 PM, Tony Lindgren wrote:
> >>>> * Vignesh R <vigneshr@...com> [170113 00:03]:
> >>>>> This patch series re enables DMA support for UART 8250_omap driver.
> >>>>>
> >>>>> Tested on AM335x, AM437x that use EDMA and OMAP5 and DRA74 EVM with
> >>>>> SDMA.
> >>>>
> >>>> Is 8250_omap serial console working for you on omap5 in general?
> >>>>
> >>>> I've noticed that it's really unresponsive for me as if the FIFO
> >>>> interrupt was not working. For example logging in might take several
> >>>> attempts and a long time with each character showing up much later
> >>>> after some timeout.
> >>>>
> >>>
> >>> Yes, I did face the same issue on omap5 using 8250_omap driver for
> >>> console. Looks like this bug has existed all along.
> >>>
> >>
> >> This looks a separate issue, I don't see any errata specific errata wrt
> >> UART on OMAP5. I will try to debug further.
> > 
> > OK maybe it's something configured or not configured by the bootloader
> > that we're missing in the Linux driver?
> > 
> 
> omap-serial uses a UART RX FIFO trigger of 1 byte whereas 8250_omap
> driver uses a RX FIFO trigger of 48 bytes. If less than 48 bytes is
> received then RX Timeout interrupt is raised which will help the driver
> to flush the FIFO. It seems like RX timeout does not seem to bring out
> UART IP from idle state on OMAP5.
> 
> I have posted a fix based on what is done for DRA7 in hwmod code:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2017-January/480619.html

OK great, thanks for fixing that! Will give it a try a bit later today.

Regards,

Tony