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SubjectRe: [PATCH v3 5/6] ARM: pinctrl: Add Broadcom Capri pinctrl driver
On 13-12-18 03:56 PM, Sherman Yin wrote:
> On 13-12-12 12:54 PM, Linus Walleij wrote:

>>> +/*
>>> + * Write to the register using the value and mask if current value
>>> is different
>>> + */
>>> +static void capri_reg_write(struct pinctrl_dev *pctldev,
>>> + void __iomem *reg,
>>> + u32 val,
>>> + u32 mask)
>>> +{
>>> + u32 old_val;
>>> + u32 new_val;
>>> +
>>> + old_val = readl(reg);
>>> + new_val = (old_val & ~mask) | (val & mask);
>>> +
>>> + if (new_val == old_val) {
>>> + dev_dbg(pctldev->dev,
>>> + "Reg 0x%p=0x%x (no change)\n",
>>> + reg, old_val);
>>> + return;
>>> + }
>>> +
>>> + dev_dbg(pctldev->dev,
>>> + "Reg 0x%p change from 0x%x to 0x%x\n",
>>> + reg, old_val, new_val);
>>> + writel(new_val, reg);
>>> +}
>>
>> This is a reimplementation of regmap for MMIO.
>> See drivers/base/regmap/regmap-mmio.c
>> Notice how regmap_update_bits() is used throughout the
>> kernel.
>>
>> If you want to do this, use regmap.
>
> Ok.

As you can see in v4 of my patchset, I've changed my driver to use the
mmio regmap. However, as I was tracing through regmap_update_bits(), it
looks like I have to go through a lot of checks and function pointers
just to do a simple write to a register. Also, I have to select
REGMAP_MMIO which brings in a bunch of code as well.

I understand the benefits of using common code, but in this case it
seems there is a lot of extra code and run-time overhead to use regmap.
In the end it also doesn't buy much in terms of functionality.

Just a quick note - it looks like the 2nd parameter of
regmap_update_bits() wants the offset of a register (offset from
regmap_mmio_context.regs). So calling the parameter "reg" is a little
confusing, at least in the MMIO case.

Regards,
Sherman


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