Re: [PATCH 4/8] serial: 8250: Handle case port doesn't have TEMT interrupt using em485.

From: Giulio Benetti <giulio.benetti@micronovasrl.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>, Kees Cook <keescook@chromium.org>,
	Matthias Brugger <mbrugger@suse.com>,
	Allen Pais <allen.lkml@gmail.com>, Sean Young <sean@mess.org>,
	Ed Blake <ed.blake@sondrel.com>,
	Stefan Potyra <Stefan.Potyra@elektrobit.com>,
	Philipp Zabel <p.zabel@pengutronix.de>,
	Joshua Scott <joshua.scott@alliedtelesis.co.nz>,
	Vignesh R <vigneshr@ti.com>,
	Rolf Evers-Fischer <rolf.evers.fischer@aptiv.com>,
	Aaron Sierra <asierra@xes-inc.com>,
	Rafael Gago <rafael.gago@gmail.com>,
	Joel Stanley <joel@jms.id.au>, Sean Wang <sean.wang@mediatek.com>,
	linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/8] serial: 8250: Handle case port doesn't have TEMT interrupt using em485.
Date: Mon, 4 Jun 2018 12:50:44 +0200	[thread overview]
Message-ID: <4a7148d5-ab2c-425d-afdc-08ddd3c522c2@micronovasrl.com> (raw)
In-Reply-To: <3a66327727d9bf2ce5adf8ef0f1fcc1fffeaa4ec.camel@linux.intel.com>

Hi,

Il 04/06/2018 12:17, Andy Shevchenko ha scritto:
> On Fri, 2018-06-01 at 14:40 +0200, Giulio Benetti wrote:
>> Some 8250 ports only have TEMT interrupt, so current implementation
>> can't work for ports without it. The only chance to make it work is to
>> loop-read on LSR register.
>>
>> With NO TEMT interrupt check if both TEMT and THRE are set looping on
>> LSR register.
> 
>> --- a/drivers/tty/serial/8250/8250_dw.c
>> +++ b/drivers/tty/serial/8250/8250_dw.c
> 
>> -		int ret = serial8250_em485_init(up);
>> +		int ret = serial8250_em485_init(up, false);
> 
> Is true for all possible DW configured types? Or it's your particular
> case?
> 

I've checked on Synopsis Designware 8250 datasheet and it's not supported.
Here is datasheet I went through:
https://linux-sunxi.org/images/d/d2/Dw_apb_uart_db.pdf

There seems not to be TEMT interrupt, I use it under sunxi SoC and on 
their datasheet(A20 for example), they don't report that interrupt too.
So it seems to be valid for all DW configured types, anyway I don't know 
how many IP reviews there could be of that peripheral.
I've tried to subscribe at Synopsis to obtain latest Datasheet but it 
ask me an active ID I don't have.

-- 
Giulio Benetti
CTO

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