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

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Message-ID: <d40d824e-1827-4030-794c-a7c7e15137e6@linux.intel.com>
Date: Mon, 21 Oct 2024 12:49:08 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Andy Shevchenko <andriy.shevchenko@...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, 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:
> > 
> > > The theory is that the so called workaround in pwr_reg_rdwr() is
> > > the actual reader of the data in 32-bit chunks. For some reason
> > > the 8-bit IO won't fail after that. Replace the workaround by using
> > > 32-bit IO explicitly and then memcpy() as much data as was requested
> > > by the user. The same approach is already in use in
> > > intel_scu_ipc_dev_command_with_size().
> 
> ...
> 
> > >  	err = intel_scu_ipc_check_status(scu);
> > > -	if (!err && id == IPC_CMD_PCNTRL_R) { /* Read rbuf */
> > > -		/* Workaround: values are read as 0 without memcpy_fromio */
> > > -		memcpy_fromio(cbuf, scu->ipc_base + 0x90, 16);
> > > -		for (nc = 0; nc < count; nc++)
> > > -			data[nc] = ipc_data_readb(scu, nc);
> > > +	if (!err) { /* Read rbuf */
> > 
> > What is the reason for the removal of that id check? This seems a clear 
> > logic change but why? And if you remove want to remove that check, what 
> > that comment then means?
> 
> Let me split this to a separate change with better explanation then.
> 
> > > +		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.

> > >  	}
> > >  	mutex_unlock(&ipclock);
> > >  	return err;
> > 
> > FYI (unrelated to this patch), there seems to be some open-coded 
> > FIELD_PREP()s in pwr_reg_rdwr(), some of which is common code between 
> > those if branches too.
> 
> This code is quite old and full of tricks that has to be tested. So, yes
> while it's possible to convert, I would like to do it in a small (baby)
> steps. This series is already quite intrusive from this perspective :-)

Yeah, no pressure, I just noted down what I saw. :-)

-- 
 i.