Re: [PATCH 0/3] tty: serial: 8250_omap: Enable DMA support

From: Vignesh R <vigneshr@ti.com>
To: Tony Lindgren <tony@atomide.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	Peter Hurley <peter@hurleysoftware.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	"linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>
Subject: Re: [PATCH 0/3] tty: serial: 8250_omap: Enable DMA support
Date: Wed, 18 Jan 2017 17:34:01 +0530	[thread overview]
Message-ID: <a3055b9c-613b-6c64-db17-05b32ec24457@ti.com> (raw)
In-Reply-To: <20170117232536.GZ7403@atomide.com>

On Wednesday 18 January 2017 04:55 AM, Tony Lindgren wrote:
> * Vignesh R <vigneshr@ti.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@ti.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

-- 
Regards
Vignesh