linux-kernel - Re: [PATCH v3 3/3] counter: 104-quad-8: Utilize helper functions to handle PR, FLAG and PSC

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Message-ID: <ZDVyJV8TfC31TYP2@smile.fi.intel.com>
Date:   Tue, 11 Apr 2023 17:43:49 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     William Breathitt Gray <william.gray@...aro.org>
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Johannes Berg <johannes.berg@...el.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v3 3/3] counter: 104-quad-8: Utilize helper functions to
 handle PR, FLAG and PSC

On Tue, Apr 11, 2023 at 10:05:25AM -0400, William Breathitt Gray wrote:
> On Tue, Apr 11, 2023 at 04:50:03PM +0300, Andy Shevchenko wrote:
> > On Mon, Apr 10, 2023 at 10:03:13AM -0400, William Breathitt Gray wrote:
> > > The Preset Register (PR), Flag Register (FLAG), and Filter Clock
> > > Prescaler (PSC) have common usage patterns. Wrap up such usage into
> > > dedicated functions to improve code clarity.

...

> > >  	*val = 0;
> > 
> > Is not needed now as always being initialized by below call.
> 
> The regmap_noinc_read() call only reads the number of bytes requested.
> Since we request 3 bytes, the upper bytes of the u64 val remain
> uninitialized, so that is why we need to set *val = 0. This isn't
> immediately clear in the code, so I can add a comment to make it
> explicit.

Hmm...
Since we are using byte array for the value, can we actually use
memset() to show that explicitly? Perhaps in that way it will be more visible?

> > >  	spin_lock_irqsave(&priv->lock, irqflags);
> > >  
> > >  	iowrite8(SELECT_RLD | RESET_BP | TRANSFER_CNTR_TO_OL, &chan->control);
> > > -
> > > -	for (i = 0; i < 3; i++)
> > > -		*val |= (unsigned long)ioread8(&chan->data) << (8 * i);
> > > +	ioread8_rep(&chan->data, val, 3);

But hold on, wouldn't this have an endianess issue? The call fills in LE,
while here you use the CPU order.

> > >  	spin_unlock_irqrestore(&priv->lock, irqflags);

That said, I think you should have something like

	u8 value[3];

	ioread8_rep(..., value, sizeof(value));

	*val = get_unaligned_le24(value);

-- 
With Best Regards,
Andy Shevchenko