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

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Date:   Wed, 8 Nov 2017 16:46:26 +0800
From:   Greentime Hu <green.hu@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Greentime <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

2017-11-08 16:36 GMT+08:00 Arnd Bergmann <arnd@...db.de>:
> 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.

Thanks. I will remove it in next version patch.

>
>> +
>> +/*
>> + * 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.

Thanks. I will remove it in next version patch.

>> 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.

Thanks. I will remove REALSHMLBA. I will consider to use 8KB or larger
page size in the next version patch.