linux-kernel - Re: Aw: Re: [PATCH v1 0/4] add syscon requirement for mt7988

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Message-ID: <20240711163855.GA2369577-robh@kernel.org>
Date: Thu, 11 Jul 2024 10:38:55 -0600
From: Rob Herring <robh@...nel.org>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: Frank Wunderlich <frank-w@...lic-files.de>,
	Frank Wunderlich <linux@...web.de>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Wim Van Sebroeck <wim@...ux-watchdog.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Daniel Golle <daniel@...rotopia.org>, linux-clk@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, linux-watchdog@...r.kernel.org
Subject: Re: Aw: Re: [PATCH v1 0/4] add syscon requirement for mt7988

On Wed, Jul 10, 2024 at 02:50:42PM +0200, AngeloGioacchino Del Regno wrote:
> Il 10/07/24 13:34, Frank Wunderlich ha scritto:
> > Hi
> > 
> > > Gesendet: Mittwoch, 10. Juli 2024 um 12:45 Uhr
> > > Von: "AngeloGioacchino Del Regno" <angelogioacchino.delregno@...labora.com>
> > > Betreff: Re: [PATCH v1 0/4] add syscon requirement for mt7988
> > > 
> > > Il 09/07/24 12:13, Frank Wunderlich ha scritto:
> > > > From: Frank Wunderlich <frank-w@...lic-files.de>
> > > > 
> > > > Some nodes require the syscon fallback at least in u-boot when using
> > > > OF_UPSTREAM.
> > > > 
> > > > This is because uboot driver uses syscon_node_to_regmap in mtk_eth.c for
> > > > "mediatek,toprgu", "mediatek,xfi_pll" and reset pointing to watchdog-node.
> > > > 
> > > 
> > > I wonder what's the major blocker here to modify the u-boot driver to take
> > > the upstream devicetree as-is, instead of using syscon_node_to_regmap?
> > 
> > in uboot there is no driver for all syscon and to handle parallel 
> > access this is done with the syscon fallback.
> > 
> > The syscon uclass is a small driver which is generic and only 
> > handle the regmap in global context.
> > 
> > In theory it could be possible that regmap is aquired twice when 
> > used from 2+ other drivers...to prevent this without
> > adding the syscon fallback each syscon needs a dedicated driver 
> > like in linux which does only syscon stuff (code
> > duplication at its best :) ).
> > 
> > of course i can use regmap_init_mem in the uboot ethernet driver
> > 
> > https://elixir.bootlin.com/u-boot/latest/source/drivers/core/regmap.c#L242
> > 
> > like it's done once for syscon-uclass.
> > 
> > but i will cause issues when a second device tries to access this 
> > regmap. So it was be much easier (for me) to add this
> > fallback and not writing 3 device-drivers in uboot doing the 
> > exactly same as syscon.
> > 
> > if you have a better idea how to handle it, let me know :)
> > 
> 
> I see. The problem is that, from your description, it looks like u-boot
> uses that as a kind of workaround for concurrent access to MMIO...
> 
> ...looks like a good topic to discuss in the u-boot mailing lists.
> 
> Definitely, the TOPRGU and the XFI PLL are not system controllers, so the actual
> "syscon" definition would be wrong for these, that's it.

While I'd prefer "syscon" never existed in the first place, I don't care 
too much if it gets added here or not. U-boot's reasoning for wanting it 
isn't really much better or worse than Linux's. Though if u-boot has 
multiple drivers using it, seems like an abstraction is missing if Linux 
doesn't need that.

Rob