Messages in this thread | | | Subject | Re: [PATCH RFC 1/3] spi: Allow SPI controller override device buswidth | From | John Garry <> | Date | Tue, 3 Mar 2020 09:42:45 +0000 |
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Hi Geert,
> > On Fri, Feb 28, 2020 at 4:23 PM John Garry <john.garry@huawei.com> wrote: >> Currently ACPI firmware description for a SPI device does not have any >> method to describe the data buswidth on the board. >> >> So even through the controller and device may support higher modes than >> standard SPI, it cannot be assumed that the board does - as such, that >> device is limited to standard SPI in such a circumstance. >> >> As a workaround, allow the controller driver supply buswidth override bits, >> which are used inform the core code that the controller driver knows the >> buswidth supported on that board for that device. > > Just wondering: can't the controller just override this (e.g. in the .setuup() > callback) without having to touch the generic code?
I think that this is a good idea.
However, where we call .setup() in spi_setup() looks a little too late - at the point we call .setup(), most of the work on vetting/fixing the mode bits is complete. And I would not want the SPI controller driver just to disregard this work and overwrite the bits (in this way).
And if we wanted to move the .setup callback earlier, then I would be worried here with 2 things: 1. Some SPI controller drivers may rely on spi->mode being set finally when .setup() is called 2. We may need to undo the work of .setup() if we later error in spi_setup(), like for invalid mode bits
However, maybe another callback could be introduced, .early_setup().
Thanks, John
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