linux-kernel - RE: [PATCH-v8] serial: 8250_dw: Add support for big-endian MMIO accesses

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Message-ID: <DB5PR02MB1141B69C5E327950511F4590D6E90@DB5PR02MB1141.eurprd02.prod.outlook.com>
Date:	Thu, 10 Dec 2015 07:26:42 +0000
From:	Noam Camus <noamc@...hip.com>
To:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"jslaby@...e.com" <jslaby@...e.com>,
	"peter@...leysoftware.com" <peter@...leysoftware.com>,
	"fransklaver@...il.com" <fransklaver@...il.com>,
	"Alexey.Brodkin@...opsys.com" <Alexey.Brodkin@...opsys.com>,
	"vgupta@...opsys.com" <vgupta@...opsys.com>
Subject: RE: [PATCH-v8] serial: 8250_dw: Add support for big-endian MMIO
 accesses

>From: Heikki Krogerus [mailto:heikki.krogerus@...ux.intel.com] 
>Sent: Wednesday, December 09, 2015 3:20 PM


>> @@ -171,7 +174,8 @@ static void dw8250_serial_out32(struct uart_port *p, int offset, int value)
>>  			if ((value & ~UART_LCR_SPAR) == (lcr & ~UART_LCR_SPAR))
>>  				return;
>>  			dw8250_force_idle(p);
>> -			writel(value, p->membase + (UART_LCR << p->regshift));
>> +			d->serial_out(value,
>> +				      p->membase + (UART_LCR << p->regshift));
>>  		}

>.. The way I see it, this is the only place where you would really need the new private serial_in/out hooks, so why not just check the >iotype here and based on that use writeb/writel/iowrite32be or what ever ..

In previous versions (V2) Greg dis-liked using iotype here this is why I added the private serial_in/serial_out

>>  static void dw8250_setup_port(struct uart_port *p)  {
>>  	struct uart_8250_port *up = up_to_u8250p(p);
>> +	struct dw8250_data *d = p->private_data;
>>  	u32 reg;
>>  
>>  	/*
>>  	 * If the Component Version Register returns zero, we know that
>>  	 * ADDITIONAL_FEATURES are not enabled. No need to go any further.
>>  	 */
>> -	reg = readl(p->membase + DW_UART_UCV);
>> +	reg = d->serial_in(p->membase + DW_UART_UCV);
>>  	if (!reg)
>>  		return;
>>  
>>  	dev_dbg(p->dev, "Designware UART version %c.%c%c\n",
>>  		(reg >> 24) & 0xff, (reg >> 16) & 0xff, (reg >> 8) & 0xff);
>>  
>> -	reg = readl(p->membase + DW_UART_CPR);
>> +	reg = d->serial_in(p->membase + DW_UART_CPR);
>>  	if (!reg)
>>  		return;

>.. Here you could as well replace the direct readl calls with serial_port_in calls.
Again, if you meant here for using iotype it was rejected.

>> @@ -390,9 +434,19 @@ static int dw8250_probe(struct platform_device 
>> *pdev)
>>  
>>  	err = device_property_read_u32(p->dev, "reg-io-width", &val);
>>  	if (!err && val == 4) {
>> -		p->iotype = UPIO_MEM32;
>> -		p->serial_in = dw8250_serial_in32;
>> -		p->serial_out = dw8250_serial_out32;
>> +		p->iotype = of_device_is_big_endian(p->dev->of_node) ?
>> +			    UPIO_MEM32BE : UPIO_MEM32;

>If this has to be tied to DT, do this check in dw8250_quirks.
Thanks , I will move this to dw8250_quirks.

>>  	dw8250_quirks(p, data);
>>  
>> +	data->serial_in = _dw8250_serial_in32;
>> +	data->serial_out = _dw8250_serial_out32;

>I don't think I understand what is going on here? You would never actually even use _dw8250_serial_in32be/out32be, no?

>Maybe I'm misunderstanding something.
This is a default in case  where "reg-io-width != 4".
What is the case you see that they are not used? (_dw8250_serial_in32be is used from dw8250_setup_port just few lines below)

-Noam
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