On Tue, Mar 08, 2011 at 11:44:48AM +0800, Shawn Guo wrote:
On Mon, Mar 07, 2011 at 10:48:10AM -0700, Grant Likely wrote:
On Mon, Mar 7, 2011 at 9:22 AM, Shawn Guo shawn.guo@linaro.org wrote:
The patch is to add all gpt, uart related dt clock nodes for babbage. It sticks to the clock name used in clock-mx51-mx53.c, so that everything gets consistent to Reference Manual. For example, the numbering in clock name usually starts from 1, while 'reg' property numbering starts from 0 to easy clock binding.
Besides the generally used clock bindings, the following properties are proposed in this patch.
- clock-alias
Like clock-outputs to reflect cl->dev_id, property clock-alias is defined to reflect cl->con_id.
This feels like leakage of Linux kernel implementation details getting encoded into the binding. There shouldn't be any need for a clock alias property. It should all just work to have multiple devices explicitly refer to the same clock node because the dt clock support patch gets first crack at resolving a struct clk pointer before clkdev does its lookup.
This is to make clk_get() work. Let's take a look at this example. i.MX28 integrates a amba-pl011 uart controller, and there are two places calling clk_get() with the same dev_id to get the different 'clk'.
static struct clk_lookup lookups[] = { /* for amba bus driver */ _REGISTER_CLOCK("duart", "apb_pclk", xbus_clk) /* for amba-pl011 driver */ _REGISTER_CLOCK("duart", NULL, uart_clk) ... };
- drivers/amba/bus.c - to get xbus_clk
static int amba_get_enable_pclk(struct amba_device *pcdev) { struct clk *pclk = clk_get(&pcdev->dev, "apb_pclk"); int ret;
pcdev->pclk = pclk; if (IS_ERR(pclk)) return PTR_ERR(pclk); ret = clk_enable(pclk); if (ret) clk_put(pclk); return ret;}
- drivers/tty/serial/amba-pl011.c - to get uart_clk
static int pl011_probe(struct amba_device *dev, struct amba_id *id) { ...
uap->clk = clk_get(&dev->dev, NULL); if (IS_ERR(uap->clk)) { ret = PTR_ERR(uap->clk); goto unmap; }... }
Will this be broken if we do not have an alias in dt clock to reflect con_id?
Sorry. The argument above is invalid, as neither dev_id nor con_id will be used to find the 'clk' when DT clock code applies. So, yes, property clock-alias is not needed.