linux-kernel - Re: [PATCH 36/41] drivers: tty: serial: 8250: store mmio resource size in port struct

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Date:   Mon, 29 Apr 2019 16:55:05 +0200
From:   "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Enrico Weigelt, metux IT consult" <info@...ux.net>
Cc:     linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
        andrew@...id.au, macro@...ux-mips.org, vz@...ia.com,
        slemieux.tyco@...il.com, khilman@...libre.com, liviu.dudau@....com,
        sudeep.holla@....com, lorenzo.pieralisi@....com,
        davem@...emloft.net, jacmet@...site.dk, linux@...sktech.co.nz,
        matthias.bgg@...il.com, linux-mips@...r.kernel.org,
        linux-serial@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-amlogic@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
        sparclinux@...r.kernel.org
Subject: Re: [PATCH 36/41] drivers: tty: serial: 8250: store mmio resource
 size in port struct

On 28.04.19 17:18, Andy Shevchenko wrote:
> On Sat, Apr 27, 2019 at 02:52:17PM +0200, Enrico Weigelt, metux IT consult wrote:
>> The io resource size is currently recomputed when it's needed but this
>> actually needs to be done once (or drivers could specify fixed values)
> 
> io -> IO

fixed.

>> Simplify that by doing this computation only once and storing the result
>> into the mapsize field. serial8250_register_8250_port() is now called
>> only once on driver init, the previous call sites now just fetch the
>> value from the mapsize field.
> 
> Do I understand correctly that this has no side effects?

I don't know of any. (except someting changes things like regshift after
the initialization phase ... :o)

>> @@ -979,6 +979,9 @@ int serial8250_register_8250_port(struct uart_8250_port *up)
>>  	if (up->port.uartclk == 0)
>>  		return -EINVAL;
>>  
>> +	/* compute the mapsize in case the driver didn't specify one */
>> +	up->mapsize = serial8250_port_size(up);
> 
> I don't know all quirks in 8250 drivers by heart, though can you guarantee that
> at this point the device reports correct IO resource size? (If I'm not mistaken
> some broken hardware needs some magic to be done before card can be properly
> handled)

Actually, I don't see anything talking to the hardware at all here.
It's all derived from values that are set up before
serial8250_register_8250_port() is called.

>> -	unsigned int size = serial8250_port_size(up);
>>  	struct uart_port *port = &up->port;
> 
>> -	int ret = 0;
> 
> This and Co is a separate change that can be done in its own patch.

I don't really understand :(
Do you mean the splitting off the retval part from the rest ?

>> +			port->membase = ioremap_nocache(port->mapbase,
>> +							port->mapsize);
> 
> You may increase readability by introducing temporary variables
> 
> 	... mapbase = port->mapbase;
> 	... mapsize = port->mapsize;
> 	...
> 	port->membase = ioremap_nocache(mapbase, mapsize);
> 	...

Is that really necessary ? Maybe it's just my personal taste, but I
don't feel the more more verbose one is really easier to read.

--mtx

-- 
Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@...ux.net -- +49-151-27565287