[PATCH 1/2] powerpc/vas: Report proper error for address translation failure

[Michael Ellerman]

Haren Myneni <haren at linux.ibm.com> writes:
> DMA controller uses CC=5 internally for translation fault handling. So
> OS should be using CC=250 and should report this error to the user space
> when NX encounters address translation failure on the request buffer.

That doesn't really explain *why* the OS must use CC=250.

Is it documented somewhere that 5 is for hardware use, and 250 is for
software?

> This patch defines CSB_CC_ADDRESS_TRANSLATION(250) and updates
> CSB.CC with this proper error code for user space.

We still have:

#define CSB_CC_TRANSLATION	(5)

And it's very unclear where one or the other should be used.

Can one or the other get a name that makes the distinction clear.

cheers


> diff --git a/Documentation/powerpc/vas-api.rst b/Documentation/powerpc/vas-api.rst
> index 1217c2f..78627cc 100644
> --- a/Documentation/powerpc/vas-api.rst
> +++ b/Documentation/powerpc/vas-api.rst
> @@ -213,7 +213,7 @@ request buffers are not in memory. The operating system handles the fault by
>  updating CSB with the following data:
>  
>  	csb.flags = CSB_V;
> -	csb.cc = CSB_CC_TRANSLATION;
> +	csb.cc = CSB_CC_ADDRESS_TRANSLATION;
>  	csb.ce = CSB_CE_TERMINATION;
>  	csb.address = fault_address;
>  
> diff --git a/arch/powerpc/include/asm/icswx.h b/arch/powerpc/include/asm/icswx.h
> index 965b1f3..b1c9a57 100644
> --- a/arch/powerpc/include/asm/icswx.h
> +++ b/arch/powerpc/include/asm/icswx.h
> @@ -77,6 +77,8 @@ struct coprocessor_completion_block {
>  #define CSB_CC_CHAIN		(37)
>  #define CSB_CC_SEQUENCE		(38)
>  #define CSB_CC_HW		(39)
> +/* User space address traslation failure */
> +#define	CSB_CC_ADDRESS_TRANSLATION	(250)
>  
>  #define CSB_SIZE		(0x10)
>  #define CSB_ALIGN		CSB_SIZE
> diff --git a/arch/powerpc/platforms/powernv/vas-fault.c b/arch/powerpc/platforms/powernv/vas-fault.c
> index 266a6ca..33e89d4 100644
> --- a/arch/powerpc/platforms/powernv/vas-fault.c
> +++ b/arch/powerpc/platforms/powernv/vas-fault.c
> @@ -79,7 +79,7 @@ static void update_csb(struct vas_window *window,
>  	csb_addr = (void __user *)be64_to_cpu(crb->csb_addr);
>  
>  	memset(&csb, 0, sizeof(csb));
> -	csb.cc = CSB_CC_TRANSLATION;
> +	csb.cc = CSB_CC_ADDRESS_TRANSLATION;
>  	csb.ce = CSB_CE_TERMINATION;
>  	csb.cs = 0;
>  	csb.count = 0;
> -- 
> 1.8.3.1