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Sender: Guenter Roeck <groeck7@gmail.com>
Date: Fri, 12 Jan 2024 11:11:07 -0800
From: Guenter Roeck <linux@roeck-us.net>
To: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>
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Subject: Re: [PATCH v11 03/10] spi: Add multi-cs memories support in SPI core
Message-ID: <3d3a11b1-8396-4d8e-9bb3-61ecb67e7efa@roeck-us.net>
References: <20231125092137.2948-1-amit.kumar-mahapatra@amd.com>
 <20231125092137.2948-4-amit.kumar-mahapatra@amd.com>
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In-Reply-To: <20231125092137.2948-4-amit.kumar-mahapatra@amd.com>

Hi,

On Sat, Nov 25, 2023 at 02:51:30PM +0530, Amit Kumar Mahapatra wrote:
> AMD-Xilinx GQSPI controller has two advanced mode that allows the
> controller to consider two flashes as one single device.
> 
> One of these two mode is the parallel mode in which each byte of data is
> stored in both devices, the even bits in the lower flash & the odd bits in
> the upper flash. The byte split is automatically handled by the QSPI
> controller.
> 
> The other mode is the stacked mode in which both the flashes share the
> same SPI bus but each of the device contain half of the data. In this mode,
> the controller does not follow CS requests but instead internally wires the
> two CS levels with the value of the most significant address bit.
> 
> For supporting both these modes SPI core need to be updated for providing
> multiple CS for a single SPI device.
> 
> For adding multi CS support the SPI device need to be aware of all the CS
> values. So, the "chip_select" member in the spi_device structure is now an
> array that holds all the CS values.
> 
> spi_device structure now has a "cs_index_mask" member. This acts as an
> index to the chip_select array. If nth bit of spi->cs_index_mask is set
> then the driver would assert spi->chip_select[n].
> 
> In parallel mode all the chip selects are asserted/de-asserted
> simultaneously and each byte of data is stored in both devices, the even
> bits in one, the odd bits in the other. The split is automatically handled
> by the GQSPI controller. The GQSPI controller supports a maximum of two
> flashes connected in parallel mode. A SPI_CONTROLLER_MULTI_CS flag bit is
> added in the spi controller flags, through ctlr->flags the spi core
> will make sure that the controller is capable of handling multiple chip
> selects at once.
> 
> For supporting multiple CS via GPIO the cs_gpiod member of the spi_device
> structure is now an array that holds the gpio descriptor for each
> chipselect.
> 
> CS GPIO is not tested on our hardware, but it has been tested by @Stefan
> https://lore.kernel.org/all/005001da1efc$619ad5a0$24d080e0$@opensource.cirrus.com/
> 

With this patch in the mainline kernel, two of my qemu emulations
(quanta-q71l-bmc and almetto-bmc) fail to instantiate the first SPI
controller and thus fail to boot from SPI. The error message is

[    3.006458] spi_master spi0: No. of CS is more than max. no. of supported CS
[    3.006775] spi_master spi0: Failed to create SPI device for /ahb/spi@1e620000/flash@0

The problem is no longer seen after reverting this patch.

Bisect log attached for reference.

Guenter

---
# bad: [70d201a40823acba23899342d62bc2644051ad2e] Merge tag 'f2fs-for-6.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs
# good: [0dd3ee31125508cd67f7e7172247f05b7fd1753a] Linux 6.7
git bisect start 'HEAD' 'v6.7'
# bad: [de927f6c0b07d9e698416c5b287c521b07694cac] Merge tag 's390-6.8-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux
git bisect bad de927f6c0b07d9e698416c5b287c521b07694cac
# bad: [35f11a3710cdcbbc5090d14017a6295454e0cc73] Merge tag 'mtd/for-6.8' of git://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux
git bisect bad 35f11a3710cdcbbc5090d14017a6295454e0cc73
# good: [d30e51aa7b1f6fa7dd78d4598d1e4c047fcc3fb9] Merge tag 'slab-for-6.8' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab
git bisect good d30e51aa7b1f6fa7dd78d4598d1e4c047fcc3fb9
# good: [fb46e22a9e3863e08aef8815df9f17d0f4b9aede] Merge tag 'mm-stable-2024-01-08-15-31' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
git bisect good fb46e22a9e3863e08aef8815df9f17d0f4b9aede
# good: [063a7ce32ddc2c4f2404b0dfd29e60e3dbcdffac] Merge tag 'lsm-pr-20240105' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/lsm
git bisect good 063a7ce32ddc2c4f2404b0dfd29e60e3dbcdffac
# bad: [f6cd66231aa58599526584ff4df1bdde8d86eac8] spi: stm32: add st,stm32mp25-spi compatible supporting STM32MP25 soc
git bisect bad f6cd66231aa58599526584ff4df1bdde8d86eac8
# good: [18f78b5e609b19b56237f0dae47068d44b8b0ecd] spi: axi-spi-engine: improvements round 2
git bisect good 18f78b5e609b19b56237f0dae47068d44b8b0ecd
# bad: [9d93c8d97b4cdb5edddb4c5530881c90eecb7e44] spi: spi-ti-qspi: switch to use modern name
git bisect bad 9d93c8d97b4cdb5edddb4c5530881c90eecb7e44
# bad: [e6b7e64cb11966b26646a362677ca5a08481157e] spi: st-ssc4: switch to use modern name
git bisect bad e6b7e64cb11966b26646a362677ca5a08481157e
# bad: [c3aeaf2f0ec8af93189488bda3928a1ac7752388] spi: pxa2xx: Use inclusive language
git bisect bad c3aeaf2f0ec8af93189488bda3928a1ac7752388
# good: [f05e2f61fe88092e0d341ea27644a84e3386358d] ALSA: hda/cs35l56: Use set/get APIs to access spi->chip_select
git bisect good f05e2f61fe88092e0d341ea27644a84e3386358d
# bad: [88a50c1663ffa9f6b31705c6bf7a887a2c8d9434] spi: Add support for stacked/parallel memories
git bisect bad 88a50c1663ffa9f6b31705c6bf7a887a2c8d9434
# bad: [4d8ff6b0991d5e86b17b235fc46ec62e9195cb9b] spi: Add multi-cs memories support in SPI core
git bisect bad 4d8ff6b0991d5e86b17b235fc46ec62e9195cb9b
# first bad commit: [4d8ff6b0991d5e86b17b235fc46ec62e9195cb9b] spi: Add multi-cs memories support in SPI core