Re: [PATCH v6 2/2] Add Intel LGM soc DMA support.

[Reddy, MallikarjunaX]

Hi Andy,
Thanks for your comments. My comments are in line.

On 9/18/2020 8:20 PM, Andy Shevchenko wrote:
> On Fri, Sep 18, 2020 at 11:42:54AM +0800, Reddy, MallikarjunaX wrote:
> > On 9/9/2020 7:14 PM, Andy Shevchenko wrote:
> > > On Wed, Sep 09, 2020 at 07:07:34AM +0800, Amireddy Mallikarjuna reddy wrote:
> ...
>
> > > > +	help
> > > > +	  Enable support for intel Lightning Mountain SOC DMA controllers.
> > > > +	  These controllers provide DMA capabilities for a variety of on-chip
> > > > +	  devices such as SSC, HSNAND and GSWIP.
> > > And how module will be called?
> >   are you expecting to include 'default y' ?
> I'm expecting to see something like "if you choose M the module will be called
> bla-foo-bar." Look at the existing examples in the kernel.
ok, i will change bool to tristate.
> ...
>
> > > > +ldma_update_bits(struct ldma_dev *d, u32 mask, u32 val, u32 ofs)
> > > > +{
> > > > +	u32 old_val, new_val;
> > > > +
> > > > +	old_val = readl(d->base +  ofs);
> > > > +	new_val = (old_val & ~mask) | (val & mask);
> > > With bitfield.h you will have this as u32_replace_bits().
> > -  new_val = (old_val & ~mask) | (val & mask);
> > + new_val = old_val;
> > + u32_replace_bits(new_val, val, mask);
> >
> > I think in this function we cant use this because of compilation issues
> > thrown by bitfield.h . Expecting 2nd and 3rd arguments as constant numbers
> > not as type variables.
> >
> > ex:
> > 	u32_replace_bits(val, 0, IPA_REG_ENDP_ROUTER_HASH_MSK_ALL);
> How comes these are constants? In the above you have a function which does
> r-m-w approach to the register. It should be something like
>
> 	old = read();
> 	new = u32_replace_bits(old, ...);
> 	write(new);
>
> > ./include/linux/bitfield.h:131:3: error: call to '__field_overflow' declared
> > with attribute error: value doesn't fit into mask
> >     __field_overflow();     \
> >     ^~~~~~~~~~~~~~~~~~
> >
> > ./include/linux/bitfield.h:119:3: error: call to '__bad_mask' declared with
> > attribute error: bad bitfield mask
> >     __bad_mask();
> >     ^~~~~~~~~~~~
> So, even with constants u32_replace_bits() must work. Maybe you didn't get how?

Thanks Andy, now i know how u32_replace_bits() is working.

The mask is not the continuous bits in some cases. Due to the mask bits 
are not continuous u32_replace_bits() can't be used here.
Ex:
        u32 mask = DMA_CPOLL_EN | DMA_CPOLL_CNT;

Comes to __field_overflow error, update bits in the 'val' are aligned 
with mask bits. Because of the this reason in u32_replace_bits() 'val'  
exceeds the 'mask' in some cases which is causing __field_overflow error.

> > > > +	if (new_val != old_val)
> > > > +		writel(new_val, d->base + ofs);
> > > > +}
> ...
>
> > > > +	/* High 4 bits */
> > > Why only 4?
> > this is higher 4 bits of 36 bit addressing..
> Make it clear in the comment.
ok.
> ...
>
> > > > +device_initcall(intel_ldma_init);
> > > Each _initcall() in general should be explained.
> > ok. is it fine?
> >
> > /* Perform this driver as device_initcall to make sure initialization
> > happens
> >   * before its dma clients of some are platform specific. make sure to
> > provice
> >   * registered dma channels and dma capabilities to client before their
> >   * initialization.
> >   */
> /*
>   * Just follow proper multi-line comment style.
>   * And use dma -> DMA.
>   */
Ok.