MIME-Version: 1.0
References: <cover.1641500561.git.christophe.jaillet@wanadoo.fr> <4a0a48fb682d13e6861f604d3cad3424672bee1f.1641500561.git.christophe.jaillet@wanadoo.fr>
In-Reply-To: <4a0a48fb682d13e6861f604d3cad3424672bee1f.1641500561.git.christophe.jaillet@wanadoo.fr>
From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 6 Jan 2022 18:06:35 -0500
Message-ID: <CAK8P3a0MfHbB8ZFuTJpbVwPLZ-9QY-MWRFGukW1S4rbBBuDRzw@mail.gmail.com>
Subject: Re: [PATCH 03/16] fpga: dfl: pci: Remove usage of the deprecated
 "pci-dma-compat.h" API
To:     Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Christoph Hellwig <hch@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>, hao.wu@intel.com,
        Tom Rix <trix@redhat.com>, Moritz Fischer <mdf@kernel.org>,
        Xu Yilun <yilun.xu@intel.com>, linux-fpga@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        kernel-janitors <kernel-janitors@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Jan 6, 2022 at 4:49 PM Christophe JAILLET
<christophe.jaillet@wanadoo.fr> wrote:
>
> In [1], Christoph Hellwig has proposed to remove the wrappers in
> include/linux/pci-dma-compat.h.
>
> Some reasons why this API should be removed have been given by Julia
> Lawall in [2].
>
> A coccinelle script has been used to perform the needed transformation.
> It can be found in [3].
>
>
> It has been hand modified to use 'dma_set_mask_and_coherent()' instead of
> 'pci_set_dma_mask()/pci_set_consistent_dma_mask()' when applicable.
> This is less verbose.
>
> The explicit 'ret = -EIO;' has been removed because
> 'dma_set_mask_and_coherent()' returns 0 or -EIO, so its return code can be
> used directly.
>
>
> [1]: https://lore.kernel.org/kernel-janitors/20200421081257.GA131897@infradead.org/
> [2]: https://lore.kernel.org/kernel-janitors/alpine.DEB.2.22.394.2007120902170.2424@hadrien/
> [3]: https://lore.kernel.org/kernel-janitors/20200716192821.321233-1-christophe.jaillet@wanadoo.fr/
>
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> Reviewed-by: Xu Yilun <yilun.xu@intel.com>

This is a correct conversion of the driver, but I'd prefer to keep this separate
from the pci-dma-compat series.

> +       ret = dma_set_mask_and_coherent(&pcidev->dev, DMA_BIT_MASK(64));
> +       if (ret)
> +               ret = dma_set_mask_and_coherent(&pcidev->dev, DMA_BIT_MASK(32));
> +       if (ret) {
>                 dev_err(&pcidev->dev, "No suitable DMA support available.\n");
>                 goto disable_error_report_exit;

The code looks a bit suspicous, both the old and the new version. If the device
ends up on a bus that can only do 32-bit DMA, shouldn't it remember this and
make sure it only does GFP_DMA32 allocations for buffers that are passed to
the device?

        Arnd