linux-kernel - Re: [PATCH 03/16] fpga: dfl: pci: Remove usage of the deprecated "pci-dma-compat.h" API

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Date:   Thu, 6 Jan 2022 18:06:35 -0500
From:   Arnd Bergmann <arnd@...db.de>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Christoph Hellwig <hch@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>, hao.wu@...el.com,
        Tom Rix <trix@...hat.com>, Moritz Fischer <mdf@...nel.org>,
        Xu Yilun <yilun.xu@...el.com>, linux-fpga@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel-janitors <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH 03/16] fpga: dfl: pci: Remove usage of the deprecated
 "pci-dma-compat.h" API

On Thu, Jan 6, 2022 at 4:49 PM Christophe JAILLET
<christophe.jaillet@...adoo.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@...adoo.fr>
> Reviewed-by: Xu Yilun <yilun.xu@...el.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