linux-kernel - Re: [PATCH V2 3/3] Adding device_dma_parameters->offset_preserve

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Date:   Tue, 2 Feb 2021 12:07:52 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jianxiong Gao <jxgao@...gle.com>
Cc:     Keith Busch <kbusch@...nel.org>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Marc Orr <marcorr@...gle.com>, Christoph Hellwig <hch@....de>,
        m.szyprowski@...sung.com, gregkh@...uxfoundation.org,
        Saravana Kannan <saravanak@...gle.com>,
        heikki.krogerus@...ux.intel.com, rafael.j.wysocki@...el.com,
        dan.j.williams@...el.com, bgolaszewski@...libre.com,
        jroedel@...e.de, iommu@...ts.linux-foundation.org,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, axboe@...com,
        sagi@...mberg.me, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 3/3] Adding device_dma_parameters->offset_preserve_mask
 to NVMe driver.

On 2021-02-02 11:21, Andy Shevchenko wrote:
> On Mon, Feb 01, 2021 at 04:25:55PM -0800, Jianxiong Gao wrote:
> 
>> +       if (dma_set_min_align_mask(dev->dev, NVME_CTRL_PAGE_SIZE - 1))
> 
> Side note: we have DMA_BIT_MASK(), please use it.

FWIW I'd actually disagree on that point. Conceptually, this is a very 
different thing from dev->{coherent_}dma_mask. It does not need to 
handle everything up to 2^64-1 correctly without overflow issues, and 
data alignments typically *are* defined in terms of sizes rather than 
numbers of bits.

In fact, it might be neat to just have callers pass a size directly to a 
dma_set_min_align() interface which asserts that it is a power of two 
and stores it as a mask internally.

Robin.

> 
>> +               dev_warn(dev->dev, "dma_set_min_align_mask failed to
>> set offset\n");
>