Re: [PATCH] USB: set device dma_mask without reference to global data

[Tony Prisk <linux-ci5G2KO2hbZ+pU9mqzGVBQ@public.gmane.org>]

On 08/05/13 10:53, Stephen Warren wrote:
> From: Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>
> Many USB host drivers contain code such as:
>
> if (!pdev->dev.dma_mask)
>          pdev->dev.dma_mask = &tegra_ehci_dma_mask;
>
> ... where tegra_ehci_dma_mask is a global. I suspect this code originated
> in commit 4a53f4e "USB: ehci-tegra: add probing through device tree" and
> was simply copied everywhere else.
>
> This works fine when the code is built-in, but can cause a crash when the
> code is in a module. The first module load sets up the dma_mask pointer,
> but if the module is removed and re-inserted, the value is now non-NULL,
> and hence is not updated to point at the new location, and hence points
> at a stale location within the previous module load address, which in
> turn causes a crash if the pointer is de-referenced.
>
> The simplest way of solving this seems to be to copy the code from
> ehci-platform.c, which uses the coherent_dma_mask as the target for the
> dma_mask pointer.
>
> Suggested-by: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
> Signed-off-by: Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
> ---
In the case of uhci-platform you would be absolutely correct. I copied the
example from tegra when we first had the problem on arch-vt8500.Because we
have no NAND support yet, I have always booted myrootfs from USB so it's
always been builtin and the problem wasnever a problem. The same problem 
would
have existed on ehci-vt8500 but Arnd replaced it with ehci-platform due to
the multiplatform issues.

for uhci-platform.c
Acked-by: Tony Prisk <linux-ci5G2KO2hbZ+pU9mqzGVBQ@public.gmane.org>

Regards
Tony P