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Date:   Tue, 25 Oct 2022 09:09:06 +0300
From:   Mika Westerberg <mika.westerberg@linux.intel.com>
To:     Mauro Lima <mauro.lima@eclypsium.com>
Cc:     broonie@kernel.org, linux-spi@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/2] intel-spi: Split hardware and software sequencing
Message-ID: <Y1d9glOgHsQlZe2L@black.fi.intel.com>
References: <20221020164508.29182-1-mauro.lima@eclypsium.com>
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In-Reply-To: <20221020164508.29182-1-mauro.lima@eclypsium.com>
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Hi,

On Thu, Oct 20, 2022 at 01:45:06PM -0300, Mauro Lima wrote:
> Right now the only driver for Intel's spi has a DANGEROUS tag for
> a bug in the past on certain Lenovo platforms. It was cleared out
> that the bug was caused for the spi software sequencing mechanism
> and if we only use the driver with the hardware sequencing
> capabilities will be much safer[1].
> 
> This changes will remove all the software sequencing bits from
> the driver and left only the hardware sequencing functionality.
> If the software sequencing capabilities are needed, the old driver
> can be build using the DANGEROUS option from the menu.
> 
> [1] https://lkml.org/lkml/2021/11/11/468
> 
> Mauro Lima (2):
>   spi: intel-spi: Move software sequencing logic outside the core
>   spi: intel-spi: build the driver with hardware sequencing by default

I'be been thinking about this and I believe we can do something simpler
instead.

All the modern "Core" CPUs expose this as PCI device and that only
supports hardware sequencer which should be safe so I think we can do
something like this:

1. Make spi-intel-pci.c to set the type to INTEL_SPI_CNL for all the
   controllers it supports (and double check that this is the case for
   all these controllers).

As a side effect the ispi->sregs will be set to NULL so the core driver
does not even try to use the software seguencer.

2. Update Kconfig of SPI_INTEL_PCI to remove "DANGEROUS" and mention in
   the help text that this only supports the hardware sequencer and only
   the modern core hardware.

3. Update Kconfig of SPI_INTEL_PLATFORM help text to mention that most
   of these are using software sequencer, leave "DANGEROUS" there.

Does this make sense? Let me know what you think. I can do this myself
as well (might take some while though since busy with other things
usual).