linux-kernel - Re: [PATCH v3 1/1] dmaengine: dw: Select only supported masters for ACPI devices

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Message-ID: <ZvFm2TOGGPa7W4rF@smile.fi.intel.com>
Date: Mon, 23 Sep 2024 16:02:17 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Serge Semin <fancer.lancer@...il.com>
Cc: dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	Viresh Kumar <vireshk@...nel.org>, Vinod Koul <vkoul@...nel.org>,
	stable@...r.kernel.org, Ferry Toth <fntoth@...il.com>
Subject: Re: [PATCH v3 1/1] dmaengine: dw: Select only supported masters for
 ACPI devices

On Mon, Sep 23, 2024 at 03:46:04PM +0300, Serge Semin wrote:
> On Mon, Sep 23, 2024 at 03:26:24PM +0300, Andy Shevchenko wrote:
> > On Mon, Sep 23, 2024 at 02:57:27PM +0300, Serge Semin wrote:
> > > On Mon, Sep 23, 2024 at 11:21:37AM +0300, Andy Shevchenko wrote:
> > > > On Mon, Sep 23, 2024 at 01:01:08AM +0300, Serge Semin wrote:
> > > > > On Fri, Sep 20, 2024 at 06:56:17PM +0300, Andy Shevchenko wrote:

...


> > Yes, I still prefer mine.
> > 
> > > But, again IMO, it seems to be
> > > better to add the default_{m,p}_master/d{p,m}_master/etc fields to the
> > > dw_dma_platform_data structure since the platform-specific controller
> > > settings have been consolidated in there. The dw_dma_chip_pdata
> > > structure looks as more like generic driver data storage.
> > 
> > I don't think that is correct place for it. The platform data is specific
> > to the DMA controller as a whole and having there the master configuration
> > will mean to have the arrays of them. This OTOH will break the OF setup
> > where this comes from the slave descriptions and may not be provided with
> > DMA controller, making it imbalanced. Yes, I may agree with you that chip data
> > is not a good place either, but at least it isolates the case to PCI + ACPI /
> > pure ACPI devices (and in particular we won't need to alter Intel Quark case).
> 
> > Ideally, we should parse the additional properties from ACPI for this kind
> > of DMA controllers to get this from the _slave_ resources. Currently this is
> > not done, but anyone may propose a such
> 
> I guess it would also mean to fix all the firmware as well, wouldn't it?

Nope, legacy will use current defaults. Only new will be more flexible.

> Do the Intel/AMD/etc ACPI firmware currently provide such a data?

I can't tell for AMD for sure, neither for Intel as a whole (not
a product related engineer). I can tell only for my experience and
I haven't known any of Intel devices with such IP that has it different.

> In anyway it would be inapplicable for the legacy hardware anyway.

Exactly!

> > (would you like to volunteer?).
> 
> not really.) Maybe in some long-distance future when I get to meet a
> device on the ACPI-based platform with the DW DMAC + some peripheral
> experiencing the denoted problem, I'll think about implementing what
> we've discussed here.

Something is telling me that this will never be needed IRL.

...

> > TL;DR: If you are okay with your authorship in v3, I prefer it over other
> > versions with the explanations given in this email thread.
> 
> Ok. Let's leave it as of your preference.

Thanks!

-- 
With Best Regards,
Andy Shevchenko