[PATCH 1/6] serial: 8250_dw: add support for clk api

Russell King - ARM Linux
2013-03-16T00:29:52Z

On Fri, Mar 15, 2013 at 09:15:11PM -0300, Emilio L?pez wrote:
> Hello Russell,
>
> El 15/03/13 19:39, Russell King - ARM Linux escribi?:
> > On Fri, Mar 15, 2013 at 09:06:23PM +0100, Maxime Ripard wrote:
> >> + /* clock got configured through clk api, all done */
> >> + if (p->uartclk)
> >
> > if (IS_ERR(p->uartclk))
> >
>
> Isn't IS_ERR for pointers? p->uartclk is an unsigned int

Right, sorry, ignore that.

> >> + return 0;
> >> +
> >> + /* try to find out clock frequency from DT as fallback */
> >> if (of_property_read_u32(np, "clock-frequency", &val)) {
> >> - dev_err(p->dev, "no clock-frequency property set\n");
> >> + dev_err(p->dev, "clk or clock-frequency not defined\n");
> >> return -EINVAL;
> >> }
> >> p->uartclk = val;
> >> @@ -294,9 +301,21 @@ static int dw8250_probe(struct platform_device *pdev)
> >> if (!uart.port.membase)
> >> return -ENOMEM;
> >>
> >> + data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
> >> + if (!data)
> >> + return -ENOMEM;
> >> +
> >> + data->clk = devm_clk_get(&pdev->dev, NULL);
> >> + if (IS_ERR(data->clk))
> >> + data->clk = NULL;
> >> + else
> >> + clk_prepare_enable(data->clk);
> >
> > if (!IS_ERR(data->clk))
> > clk_prepare_enable(data->clk);
> >
>
> See below
>
> >> +
> >> uart.port.iotype = UPIO_MEM;
> >> uart.port.serial_in = dw8250_serial_in;
> >> uart.port.serial_out = dw8250_serial_out;
> >> + uart.port.private_data = data;
> >> + uart.port.uartclk = clk_get_rate(data->clk);
> >
> > What if data->clk is invalid?
> >
> > if (!IS_ERR(data->clk)
> > uart.port.uartclk = clk_get_rate(data->clk);
> >
>
> I'm not sure if it is coincidental or the way it is supposed to be, but
> when using the common clock framework, if you pass a NULL to
> clk_get_rate, the function explicitly checks for it and returns 0. I
> relied on that behaviour when implementing this; see the if..else block
> above. Is this not always the case on other clock drivers?

That's something that the common clock framework decided to do. It's
not a defined part of the API though, so drivers shouldn't rely on
this behaviour meaning anything special.