On 05/26/13 15:21, Maxime Ripard wrote:
+static void sunxi_i2c_write(struct sunxi_i2c_dev *i2c_dev, u16 reg, u8 value)
+{
+ writel(value, i2c_dev->membase + reg);
Why writel? and why without (u32)value? I thought iowrite* where the
preferred calls and in this case, wouldn't we want writeb since
value is u8?
You're right, value should be a u32 here, thanks for noticing.
For the iowrite* vs write*, there's no consensus, and as such no
preferred way. write* functions are doing an MMIO only access,
while iowrite functions can do MMIO and port I/O accesses.
Note that it doesn't change anything on ARM, since there's no port IO on
ARM.
Ah I see, missinformation on my end. Sorry.
But why write 32 bits? The register is only 8 wide, with the rest being
'reserved'. Then again, the register IS 32 bits wide and probably will
haev 32 bits written to it? Correct?
+}
+
+static u32 sunxi_i2c_read(struct sunxi_i2c_dev *i2c_dev, u16 reg)
+{
+ return readl(i2c_dev->membase + reg);
And here, readl does match the return of u32, but aren't we always
reading 8 bits since the TWI Data Register only uses the first 8
bits?
So wouldn't we want to return u8 and readb?
They are meant to be general purpose accessors, so we shouldn't focus
only on the data register.
Ah yes, of course.
+static int sunxi_i2c_probe(struct platform_device *pdev)
+{
+ struct sunxi_i2c_dev *i2c_dev;
+ struct device_node *np;
+ u32 freq, div_m, div_n;
+ struct resource res;
I feel stupid for questioning this, since it only shows my lack of
knowledge, but
If you declare all the memory here, isn't all the data lost after
exiting the _probe function? we pass a pointer to this memory in the
of_address_to_resource() function so that fills it, right?
Or does after devm_ioremap_resource it no longer matter, since that
function got what it needed and useless after?
The struct resource is only there to declare the base address and the
size of memory address. Once we have mapped it, we don't care about it
anymore.
Thanks for clarifying that, I will adapt my driver to do the same.
Maxime
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