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

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Message-ID: <CAPLW+4kTUmG=uPQadJC5pyfDvydvr1dKnJY6UxQva2Ch-x7v3g@mail.gmail.com>
Date: Fri, 26 Jan 2024 13:23:24 -0600
From: Sam Protsenko <semen.protsenko@...aro.org>
To: Mark Brown <broonie@...nel.org>
Cc: Tudor Ambarus <tudor.ambarus@...aro.org>, andi.shyti@...nel.org, arnd@...db.de, 
	robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org, 
	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@...r.kernel.org, andre.draszik@...aro.org, 
	peter.griffin@...aro.org, kernel-team@...roid.com, willmcvicker@...gle.com
Subject: Re: [PATCH v2 23/28] spi: s3c64xx: retrieve the FIFO size from the
 device tree

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},

And I'm pretty sure the comment (in struct s3c64xx_spi_port_config)
for .fifo_lvl_mask field is not correct anymore:

     * @fifo_lvl_mask: Bit-mask for {TX|RX}_FIFO_LVL bits in
SPI_STATUS register.

Maybe it used to indicate the bit number in SPI_STATUS register for
{TX|RX}_FIFO_LVL fields, but not anymore. Nowadays it looks like
fifo_lvl_mask just specifies FIFO depth for each IP instance.