Received-SPF: pass (google.com: domain of linux-kernel+bounces-32153-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Sender: Guenter Roeck <groeck7@gmail.com>
Message-ID: <ed1de0d4-9a88-47b1-a280-b872f6fdecb6@roeck-us.net>
Date: Sun, 21 Jan 2024 11:29:48 -0800
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v11 03/10] spi: Add multi-cs memories support in SPI core
Content-Language: en-US
To: Michael Walle <michael@walle.cc>
Cc: Mark Brown <broonie@kernel.org>,
 Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>,
 tudor.ambarus@linaro.org, pratyush@kernel.org, miquel.raynal@bootlin.com,
 richard@nod.at, vigneshr@ti.com, sbinding@opensource.cirrus.com,
 lee@kernel.org, james.schulman@cirrus.com, david.rhodes@cirrus.com,
 rf@opensource.cirrus.com, perex@perex.cz, tiwai@suse.com,
 linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org,
 linux-mtd@lists.infradead.org, nicolas.ferre@microchip.com,
 alexandre.belloni@bootlin.com, claudiu.beznea@tuxon.dev,
 michal.simek@amd.com, linux-arm-kernel@lists.infradead.org,
 alsa-devel@alsa-project.org, patches@opensource.cirrus.com,
 linux-sound@vger.kernel.org, git@amd.com, amitrkcian2002@gmail.com
References: <20231125092137.2948-1-amit.kumar-mahapatra@amd.com>
 <20231125092137.2948-4-amit.kumar-mahapatra@amd.com>
 <3d3a11b1-8396-4d8e-9bb3-61ecb67e7efa@roeck-us.net>
 <d3c93c4c-3754-480c-84c2-9455ec8af702@roeck-us.net>
 <Zaxtm0JlQYU0/K/v@finisterre.sirena.org.uk>
 <ec7e7972-d48d-4a47-bd03-eec0c4334471@roeck-us.net>
 <9806d99fab46c928f337b30b21057b3e@walle.cc>
From: Guenter Roeck <linux@roeck-us.net>
Autocrypt: addr=linux@roeck-us.net; keydata=
 xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN
 RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7
 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl
 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh
 gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX
 IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC
 kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0
 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s
 jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk
 BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv
 ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL
 CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAlVcphcFCRmg06EACgkQyx8mb86fmYFg0RAA
 nzXJzuPkLJaOmSIzPAqqnutACchT/meCOgMEpS5oLf6xn5ySZkl23OxuhpMZTVX+49c9pvBx
 hpvl5bCWFu5qC1jC2eWRYU+aZZE4sxMaAGeWenQJsiG9lP8wkfCJP3ockNu0ZXXAXwIbY1O1
 c+l11zQkZw89zNgWgKobKzrDMBFOYtAh0pAInZ9TSn7oA4Ctejouo5wUugmk8MrDtUVXmEA9
 7f9fgKYSwl/H7dfKKsS1bDOpyJlqhEAH94BHJdK/b1tzwJCFAXFhMlmlbYEk8kWjcxQgDWMu
 GAthQzSuAyhqyZwFcOlMCNbAcTSQawSo3B9yM9mHJne5RrAbVz4TWLnEaX8gA5xK3uCNCeyI
 sqYuzA4OzcMwnnTASvzsGZoYHTFP3DQwf2nzxD6yBGCfwNGIYfS0i8YN8XcBgEcDFMWpOQhT
 Pu3HeztMnF3HXrc0t7e5rDW9zCh3k2PA6D2NV4fews9KDFhLlTfCVzf0PS1dRVVWM+4jVl6l
 HRIAgWp+2/f8dx5vPc4Ycp4IsZN0l1h9uT7qm1KTwz+sSl1zOqKD/BpfGNZfLRRxrXthvvY8
 BltcuZ4+PGFTcRkMytUbMDFMF9Cjd2W9dXD35PEtvj8wnEyzIos8bbgtLrGTv/SYhmPpahJA
 l8hPhYvmAvpOmusUUyB30StsHIU2LLccUPPOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq
 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7
 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM
 J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi
 pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz
 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w
 ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF
 I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT
 nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY
 HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX
 JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAlVcpi8FCRmg08MACgkQyx8mb86fmYHNRQ/+
 J0OZsBYP4leJvQF8lx9zif+v4ZY/6C9tTcUv/KNAE5leyrD4IKbnV4PnbrVhjq861it/zRQW
 cFpWQszZyWRwNPWUUz7ejmm9lAwPbr8xWT4qMSA43VKQ7ZCeTQJ4TC8kjqtcbw41SjkjrcTG
 wF52zFO4bOWyovVAPncvV9eGA/vtnd3xEZXQiSt91kBSqK28yjxAqK/c3G6i7IX2rg6pzgqh
 hiH3/1qM2M/LSuqAv0Rwrt/k+pZXE+B4Ud42hwmMr0TfhNxG+X7YKvjKC+SjPjqp0CaztQ0H
 nsDLSLElVROxCd9m8CAUuHplgmR3seYCOrT4jriMFBtKNPtj2EE4DNV4s7k0Zy+6iRQ8G8ng
 QjsSqYJx8iAR8JRB7Gm2rQOMv8lSRdjva++GT0VLXtHULdlzg8VjDnFZ3lfz5PWEOeIMk7Rj
 trjv82EZtrhLuLjHRCaG50OOm0hwPSk1J64R8O3HjSLdertmw7eyAYOo4RuWJguYMg5DRnBk
 WkRwrSuCn7UG+qVWZeKEsFKFOkynOs3pVbcbq1pxbhk3TRWCGRU5JolI4ohy/7JV1TVbjiDI
 HP/aVnm6NC8of26P40Pg8EdAhajZnHHjA7FrJXsy3cyIGqvg9os4rNkUWmrCfLLsZDHD8FnU
 mDW4+i+XlNFUPUYMrIKi9joBhu18ssf5i5Q=
In-Reply-To: <9806d99fab46c928f337b30b21057b3e@walle.cc>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit

On 1/21/24 10:06, Michael Walle wrote:
>>>> FWIW, the problem is due to
>>>
>>>> +#define SPI_CS_CNT_MAX 4
>>>
>>>> in the offending patch, but apeed2400 FMC supports up to 5 SPI chip selects.
>>>>
>>>>   static const struct aspeed_spi_data ast2400_fmc_data = {
>>>>          .max_cs        = 5,
>>>>     ^^^^^^^^^^^^^^^^^^^
>>>>          .hastype       = true,
>>>
>>>> Limiting .max_cs to 4 or increasing SPI_CS_CNT_MAX to 5 fixes the problem,
>>>> though of course I don't know if increasing SPI_CS_CNT_MAX has other side
>>>> effects.
>>>
>>> Yeah, I was coming to a similar conclusion myself - the limit is just
>>> too low.  I can't see any problem with increasing it.
>>
>> It would cost a bit of memory and somewhat affect performance sine many
>> of the newly introduced loops are bound by SPI_CS_CNT_MAX and not by
>> num_chipselect.
>>
>> It also might make sense to document the new limit somewhere. Prior
>> to this commit it was not limited at all.
>> Documentation/devicetree/bindings/spi/spi-davinci.txt lists 5 chip
>> selects in its example for the use of cs-gpios.
>> Documentation/devicetree/bindings/spi/spi-controller.yaml also does not
>> list a limit.
> 
> Given that, that the rest of this series is under discussion (and esp. whether
> it is the correct way to do it) it might make sense to just revert the picked
> patches.
> 

I can't really comment on that, but I found that there is another
affected devicetree property: num-cs. Its range isn't limited in
Documentation/devicetree/bindings/spi/spi-controller.yaml. Various
dts/dtsi files use numbers as large as 8. The range is limited in some
bindings files, but not all of them.
Documentation/devicetree/bindings/spi/spi-lantiq-ssc.txt, for example,
says

   "num-cs: see spi-bus.txt, set to 8 if unset"

Various Broadcom dtsi files set it to 8.

So I guess 8 would be the absolute minimum to re-enable support for
affected systems.

Guenter