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

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Date: Mon, 5 Feb 2024 11:54:03 +0200
From: Tudor Ambarus <tudor.ambarus@...aro.org>
To: Sam Protsenko <semen.protsenko@...aro.org>, Arnd Bergmann <arnd@...db.de>
Cc: Mark Brown <broonie@...nel.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 26.01.2024 22:20, Sam Protsenko wrote:
> On Fri, Jan 26, 2024 at 2:17 PM Arnd Bergmann <arnd@...db.de> wrote:
>>
>> 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.
>>
> 
> Exactly. I guess that's exactly what Tudor mentioned in his commit
> message, and he's trying to fix that very problem by relying on
> corresponding dts property (in his patch series) rather than on
> .fifo_lvl_mask.
> 

Yes, all from above are correct. I'll split the FIFO size patches into a
smaller series to be easier to review.

Cheers,
ta