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

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Message-ID: <23369ea1-12d2-4386-a8ac-431620b75e2e@collabora.com>
Date: Wed, 10 Jul 2024 14:50:42 +0200
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Frank Wunderlich <frank-w@...lic-files.de>
Cc: Frank Wunderlich <linux@...web.de>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>, Rob Herring <robh@...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

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.

Cheers

> regards Frank
> 
>> Regards,
>> Angelo
>