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

From: Reddy, MallikarjunaX
Date: Mon Sep 21 2020 - 11:13:33 EST

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.

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, ...);

./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
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.
        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.


Each _initcall() in general should be explained.
ok. is it fine?

/* Perform this driver as device_initcall to make sure initialization
 * before its dma clients of some are platform specific. make sure to
 * registered dma channels and dma capabilities to client before their
 * initialization.
* Just follow proper multi-line comment style.
* And use dma -> DMA.