linux-kernel - Re: [PATCH v2 1/3] platform/x86: intel_scu

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Message-ID: <ZxYmxOPLOGol22gz@smile.fi.intel.com>
Date: Mon, 21 Oct 2024 13:02:44 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
	platform-driver-x86@...r.kernel.org,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Hans de Goede <hdegoede@...hat.com>, Ferry Toth <fntoth@...il.com>
Subject: Re: [PATCH v2 1/3] platform/x86: intel_scu_ipc: Replace workaround
 by 32-bit IO

On Mon, Oct 21, 2024 at 12:54:16PM +0300, Andy Shevchenko wrote:
> On Mon, Oct 21, 2024 at 12:49:08PM +0300, Ilpo Järvinen wrote:
> > On Mon, 21 Oct 2024, Andy Shevchenko wrote:
> > > On Mon, Oct 21, 2024 at 12:24:57PM +0300, Ilpo Järvinen wrote:
> > > > On Mon, 21 Oct 2024, Andy Shevchenko wrote:

...

> > > > > +		for (nc = 0, offset = 0; nc < 4; nc++, offset += 4)
> > > > > +			wbuf[nc] = ipc_data_readl(scu, offset);
> > > > > +		memcpy(data, wbuf, count);
> > > > 
> > > > So do we actually need to read more than
> > > > DIV_ROUND_UP(min(count, 16U), sizeof(u32))? Because that's the approach 
> > > > used in intel_scu_ipc_dev_command_with_size() which you referred to.
> > > 
> > > I'm not sure I follow. We do IO for whole (16-bytes) buffer, but return only
> > > asked _bytes_ to the user.
> > 
> > So always reading 16 bytes is not part of the old workaround? Because it 
> > has a "lets read enough" feel.
> 
> Ah, now I got it! Yes, we may reduce the reads to just needed ones.
> The idea is that we always have to perform 32-bit reads independently
> on the amount of data we want.

Oh, looking at the code (*) it seems they are really messed up in the original
with bytes vs. 32-bit words! Since the above has been tested, let me put this
on TODO list to clarify this mess and run with another testing.

Sounds good to you?

*) the mythical comment about max 5 items for 20-byte buffer is worrying and
now I know why,

-- 
With Best Regards,
Andy Shevchenko