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 <20240125145007.748295-24-tudor.ambarus@linaro.org>
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Date: Fri, 26 Jan 2024 21:16:53 +0100
From: "Arnd Bergmann" <arnd@arndb.de>
To: "Sam Protsenko" <semen.protsenko@linaro.org>,
 "Mark Brown" <broonie@kernel.org>
Cc: "Tudor Ambarus" <tudor.ambarus@linaro.org>,
 "Andi Shyti" <andi.shyti@kernel.org>, "Rob Herring" <robh+dt@kernel.org>,
 krzysztof.kozlowski+dt@linaro.org, "Conor Dooley" <conor+dt@kernel.org>,
 "Alim Akhtar" <alim.akhtar@samsung.com>, linux-spi@vger.kernel.org,
 linux-samsung-soc@vger.kernel.org, devicetree@vger.kernel.org,
 linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
 Linux-Arch <linux-arch@vger.kernel.org>,
 =?UTF-8?Q?Andr=C3=A9_Draszik?= <andre.draszik@linaro.org>,
 "Peter Griffin" <peter.griffin@linaro.org>, kernel-team@android.com,
 "William McVicker" <willmcvicker@google.com>
Subject: Re: [PATCH v2 23/28] spi: s3c64xx: retrieve the FIFO size from the device tree
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On Fri, Jan 26, 2024, at 20:23, Sam Protsenko wrote:
> On Thu, Jan 25, 2024 at 11:33=E2=80=AFAM Mark Brown <broonie@kernel.or=
g> 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 =3D { 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