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

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Date:   Mon, 4 Jun 2018 12:50:44 +0200
From:   Giulio Benetti <giulio.benetti@...ronovasrl.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jslaby@...e.com>, Kees Cook <keescook@...omium.org>,
        Matthias Brugger <mbrugger@...e.com>,
        Allen Pais <allen.lkml@...il.com>, Sean Young <sean@...s.org>,
        Ed Blake <ed.blake@...drel.com>,
        Stefan Potyra <Stefan.Potyra@...ktrobit.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Joshua Scott <joshua.scott@...iedtelesis.co.nz>,
        Vignesh R <vigneshr@...com>,
        Rolf Evers-Fischer <rolf.evers.fischer@...iv.com>,
        Aaron Sierra <asierra@...-inc.com>,
        Rafael Gago <rafael.gago@...il.com>,
        Joel Stanley <joel@....id.au>,
        Sean Wang <sean.wang@...iatek.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] serial: 8250: Handle case port doesn't have TEMT
 interrupt using em485.

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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