Re: [PATCH v2] spi: Fix regression when the SPI controller does not pass max_speed_hz

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

Hi Fabio,

On Tue, Dec 29, 2020 at 5:06 AM Fabio Estevam <festevam@xxxxxxxxx> wrote:
> Since commit 9326e4f1e5dd ("spi: Limit the spi device max speed to
> controller's max speed") the following regression is observed on an
> imx6q-sabresd:
>
> [    3.918284] spi_imx 2008000.spi: cannot set clock freq: 0 (base freq: 60000000)
> [    3.925953] Division by zero in kernel.
> [    3.929831] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W         5.10.0-next-20201223 #276
> [    3.938565] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
> [    3.945124] [<c0111a68>] (unwind_backtrace) from [<c010c068>] (show_stack+0x10/0x14)
> [    3.952925] [<c010c068>] (show_stack) from [<c0e11540>] (dump_stack+0xe0/0x10c)
> [    3.960279] [<c0e11540>] (dump_stack) from [<c05d471c>] (Ldiv0+0x8/0x10)
> [    3.967026] [<c05d471c>] (Ldiv0) from [<c089b044>] (mx51_ecspi_prepare_transfer+0xfc/0x17c)
>
> The spi-imx driver does not fill the max_speed_hz field, so we get:
>
> spi->max_speed_hz = 20MHz
> spi->controller->max_speed_hz = 0MHz
>
> which will result in spi->max_speed_hz being 0, causing the division by
> zero in the spi-imx driver.
>
> Fix this problem, by checking if spi->controller->max_speed_hz is not
> zero prior to assign it to spi->max_speed_hz.
>
> Fixes: 9326e4f1e5dd ("spi: Limit the spi device max speed to controller's max speed")
> Signed-off-by: Fabio Estevam <festevam@xxxxxxxxx>

See also
https://lore.kernel.org/linux-spi/20201216092321.413262-1-tudor.ambarus@xxxxxxxxxxxxx/

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds