U-Boot SPI DM framework issues
sjg at chromium.org
Tue Jul 12 12:59:05 CEST 2022
On Mon, 11 Jul 2022 at 09:52, Andre Przywara <andre.przywara at arm.com> wrote:
> while trying to debug some nasty SPI flash issue on sunxi, I came
> across some oddities in the SPI DM framework, and wanted to check some
> things, since I am not sure whether I miss things here:
> - When I do a simple "sf probe" call, I see *two* calls to the .claim_bus
> callback: the first one from:
> drivers/mtd/spi/sf_probe.c:spi_flash_probe_slave(), which is
> expected, but then also, shortly afterwards, a second call from:
> After the probe operation finished, I see the corresponding
> two spi_release_bus() calls. Seeing *two* claim calls in that nested
> way looks rather odd, and the name *claim* sounds like it should be only
> one slave device/driver being able to, well, claim the bus.
> From digging through the code it looks like we call spi_mem_exec_op()
> only from *inside* drivers that already claimed the bus, so shall we
> drop the call inside spi_mem_exec_op()?
> Allowing those nested calls has some consequences for the
> implementation of .claim_bus in the controller drivers, as it does not
> sound indicated to enabled/disable hardware in there. Enabling clock
> gates *again* might not be harmful per se, but if the first .release_bus
> call already disables clocks and resets, this might cause problems.
> - In many controller drivers I see the .of_to_plat implementation checking
> for a "spi-max-frequency" property in the *controller's* DT node, mostly
> with a fallback value, and using that frequency as an upper bus
> frequency limit for the whole controller operation. But looking at the
> official DT bindings, this property is supposed to be a *slave device*
> property, and indeed checking a few dozen .dts file I see it only being
> used in *child* nodes of SPI controllers, never in controller nodes.
> There is some proper usage in
> drivers/spi/spi-uclass.c:spi_slave_of_to_plat(), but to me it looks like
> the bus node code is wrong and should be removed, from the other
> invocation in spi-uclass.c and all the controller drivers.
> For sunxi (and probably others) this has the consequence of limiting the
> whole bus to some "default" frequency limit, which is rather low:
> #define SUN4I_SPI_DEFAULT_RATE 1000000
> plat->max_hz = fdtdec_get_int(gd->fdt_blob, node,
> So we never go beyond this 1 MHz, even though the SPI flash chips
> explicitly advertise 40MHz or more in their child nodes.
> Please let me know if I am missing something here! If not, I am happy to
> send some patches aiming at fixing those things.
This all sounds right to me and patches are welcome.
Re the first issue, I suspect something went haywire with the spimem conversion.
For the second, the binding predates Linux (I think?) so it would be
good to tidy this up.
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