linux-kernel - Re: [PATCH v3 08/12] arm64: dts: exynos: gs101: remove reg-io-width from serial

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Date: Wed, 17 Jan 2024 14:59:24 +0000
From: Tudor Ambarus <tudor.ambarus@...aro.org>
To: Sam Protsenko <semen.protsenko@...aro.org>
Cc: peter.griffin@...aro.org, krzysztof.kozlowski+dt@...aro.org,
 gregkh@...uxfoundation.org, mturquette@...libre.com, sboyd@...nel.org,
 robh+dt@...nel.org, conor+dt@...nel.org, andi.shyti@...nel.org,
 alim.akhtar@...sung.com, jirislaby@...nel.org, s.nawrocki@...sung.com,
 tomasz.figa@...il.com, cw00.choi@...sung.com,
 linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org,
 linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
 linux-serial@...r.kernel.org, andre.draszik@...aro.org,
 kernel-team@...roid.com, willmcvicker@...gle.com
Subject: Re: [PATCH v3 08/12] arm64: dts: exynos: gs101: remove reg-io-width
 from serial



On 1/16/24 17:57, Sam Protsenko wrote:
> On Tue, Jan 9, 2024 at 7:00 AM Tudor Ambarus <tudor.ambarus@...aro.org> wrote:
>> Remove the reg-io-width property in order to comply with the bindings.
>>
>> The entire bus (PERIC) on which the GS101 serial resides only allows
>> 32-bit register accesses. The reg-io-width dt property is disallowed
>> for the "google,gs101-uart" compatible and instead the iotype is
>> inferred from the compatible.
>>
>> Reviewed-by: Peter Griffin <peter.griffin@...aro.org>
>> Signed-off-by: Tudor Ambarus <tudor.ambarus@...aro.org>
>> ---
> Reviewed-by: Sam Protsenko <semen.protsenko@...aro.org>
> 
> Just out of curiosity (I probably missed the relevant discussion
> earlier): what is the actual reason for moving 'reg-io-width' to the
> driver's code as 'iotype'? I mean, what is the actual problem that's

The majority (if not all?) of the hardware blocks in GS101 SoC require
32 bit register access widths. Instead of specifying reg-io-width = 4
everywhere in the device tree, we infer it from the compatibles.

The relevant discussion is here:
https://lore.kernel.org/linux-arm-kernel/db368449-f446-47e8-81b6-a11c2a872306@linaro.org/

Cheers,
ta

> being solved by this -- is it to make the earlycon functional for
> gs101? I'm asking because the bus width looks like a part of HW
> description, which usually belongs to dts, from the design point of
> view. Anyways, that's not a concern, just trying to understand the
> decision.