linux-kernel - Re: [PATCH v2 23/28] spi: s3c64xx: retrieve the FIFO size from the device tree

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Message-Id: <e4b76c3d-f710-4b32-aa30-23cb54346d15@app.fastmail.com>
Date: Fri, 26 Jan 2024 21:16:53 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Sam Protsenko" <semen.protsenko@...aro.org>,
 "Mark Brown" <broonie@...nel.org>
Cc: "Tudor Ambarus" <tudor.ambarus@...aro.org>,
 "Andi Shyti" <andi.shyti@...nel.org>, "Rob Herring" <robh+dt@...nel.org>,
 krzysztof.kozlowski+dt@...aro.org, "Conor Dooley" <conor+dt@...nel.org>,
 "Alim Akhtar" <alim.akhtar@...sung.com>, linux-spi@...r.kernel.org,
 linux-samsung-soc@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 Linux-Arch <linux-arch@...r.kernel.org>,
 André Draszik <andre.draszik@...aro.org>,
 "Peter Griffin" <peter.griffin@...aro.org>, kernel-team@...roid.com,
 "William McVicker" <willmcvicker@...gle.com>
Subject: Re: [PATCH v2 23/28] spi: s3c64xx: retrieve the FIFO size from the device tree

On Fri, Jan 26, 2024, at 20:23, Sam Protsenko wrote:
> On Thu, Jan 25, 2024 at 11:33 AM Mark Brown <broonie@...nel.org> wrote:
>>
>> On Thu, Jan 25, 2024 at 02:50:01PM +0000, Tudor Ambarus wrote:
>>
>> > Allow SoCs that have multiple instances of the SPI IP with different
>> > FIFO sizes to specify their FIFO size via the "samsung,spi-fifosize"
>> > device tree property. With this we can break the dependency between the
>> > SPI alias, the fifo_lvl_mask and the FIFO size.
>>
>> OK, so we do actually have SoCs with multiple instances of the IP with
>> different FIFO depths (and who knows what else other differences)?
>
> I think that's why we can see .fifo_lvl_mask[] with different values
> for different IP instances. For example, ExynosAutoV9 has this (in
> upstream driver, yes):
>
>     .fifo_lvl_mask = { 0x1ff, 0x1ff, 0x7f, 0x7f, 0x7f, 0x7f, 0x1ff,
> 0x7f, 0x7f, 0x7f, 0x7f, 0x7f},
>

That sounds like the same bug as in the serial port driver,
by assuming that the alias values in the devicetree have
a particular meaning in identifying instances. This immediately
breaks when there is a dtb file that does not use the same
alias values, e.g. because it only needs some of the SPI
ports.

      Arnd