linux-kernel - Re: [PATCH 05/31] nds32: MMU definitions

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Date:   Wed, 8 Nov 2017 09:36:18 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Greentime Hu <green.hu@...il.com>
Cc:     greentime@...estech.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Networking <netdev@...r.kernel.org>,
        Vincent Chen <vincentc@...estech.com>
Subject: Re: [PATCH 05/31] nds32: MMU definitions

On Wed, Nov 8, 2017 at 6:54 AM, Greentime Hu <green.hu@...il.com> wrote:

> +/*
> + * The DMA mask corresponding to the maximum bus address allocatable
> + * using GFP_DMA.  The default here places no restriction on DMA
> + * allocations.  This must be the smallest DMA mask in the system,
> + * so a successful GFP_DMA allocation will always satisfy this.
> + */
> +#ifndef ISA_DMA_THRESHOLD
> +#define ISA_DMA_THRESHOLD      (0xffffffffULL)
> +#endif

I see this one only in powerpc, I think it can be removed.

> +
> +/*
> + * Optional device DMA address remapping. Do _not_ use directly!
> + * We should really eliminate virt_to_bus() here - it's deprecated.
> + */
> +#define page_to_dma(dev, page)         ((dma_addr_t)__virt_to_phys((unsigned long)page_address(page)))
> +#define dma_to_virt(dev, addr)         ((void *)__phys_to_virt(addr))
> +#define virt_to_dma(dev, addr)         ((dma_addr_t)__virt_to_phys((unsigned long)(addr)))

This looks like an older comment, I think we have eliminated them from the
mainline kernel in all drivers, so you should remove them here too.

> diff --git a/arch/nds32/include/asm/shmparam.h b/arch/nds32/include/asm/shmparam.h
> new file mode 100644
> index 0000000..5679648
> --- /dev/null
> +++ b/arch/nds32/include/asm/shmparam.h

> +
> +/*
> + * This should be the size of the virtually indexed cache/ways,
> + * whichever is greater since the cache aliases every size/ways
> + * bytes.
> + */
> +#define        SHMLBA  (4 * PAGE_SIZE) /* attach addr a multiple of this */
> +#define        REALSHMLBA      SHMLBA

I don't see REALSHMLBA anywhere in the kernel, do you need it?

For SHMLBA, I think it should be defined as an absolute number, using
the maximum
that you might need for any possible value of PAGE_SIZE. Otherwise user space
has a much harder time figuring out what it should use.

        Arnd