linux-kernel - Re: [PATCH v7 02/15] swiotlb: Refactor swiotlb_create

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Date:   Thu, 27 May 2021 15:24:42 +0200
From:   Christoph Hellwig <hch@....de>
To:     Claire Chang <tientzu@...omium.org>
Cc:     Rob Herring <robh+dt@...nel.org>, mpe@...erman.id.au,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        benh@...nel.crashing.org, paulus@...ba.org,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        sstabellini@...nel.org, Robin Murphy <robin.murphy@....com>,
        grant.likely@....com, xypron.glpk@....de,
        Thierry Reding <treding@...dia.com>, mingo@...nel.org,
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        Greg KH <gregkh@...uxfoundation.org>,
        Saravana Kannan <saravanak@...gle.com>,
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        Randy Dunlap <rdunlap@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
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Subject: Re: [PATCH v7 02/15] swiotlb: Refactor swiotlb_create_debugfs

On Tue, May 18, 2021 at 02:42:02PM +0800, Claire Chang wrote:
>  struct io_tlb_mem *io_tlb_default_mem;
> +static struct dentry *debugfs_dir;
>  
>  /*
>   * Max segment that we can provide which (if pages are contingous) will
> @@ -662,18 +663,30 @@ EXPORT_SYMBOL_GPL(is_swiotlb_active);
>  
>  #ifdef CONFIG_DEBUG_FS
>  
> +static void swiotlb_create_debugfs(struct io_tlb_mem *mem, const char *name)
>  {
>  	if (!mem)
> +		return;

I don't think this check makes much sense here.

> +}
> +
> +static int __init swiotlb_create_default_debugfs(void)
> +{
> +	struct io_tlb_mem *mem = io_tlb_default_mem;
> +
> +	if (mem) {
> +		swiotlb_create_debugfs(mem, "swiotlb");
> +		debugfs_dir = mem->debugfs;
> +	} else {
> +		debugfs_dir = debugfs_create_dir("swiotlb", NULL);
> +	}

This also looks rather strange.  I'd much rather create move the
directory creation of out swiotlb_create_debugfs.  E.g. something like:

static void swiotlb_create_debugfs_file(struct io_tlb_mem *mem)
{
	debugfs_create_ulong("io_tlb_nslabs", 0400, mem->debugfs, &mem->nslabs);
	debugfs_create_ulong("io_tlb_used", 0400, mem->debugfs, &mem->used);
}

static int __init swiotlb_init_debugfs(void)
{
	debugfs_dir = debugfs_create_dir("swiotlb", NULL);
	if (io_tlb_default_mem) {
		io_tlb_default_mem->debugfs = debugfs_dir;
		swiotlb_create_debugfs_files(io_tlb_default_mem);
	}
	return 0;
}
late_initcall(swiotlb_init_debugfs);

...

static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
                                    struct device *dev)
{
	...
		mem->debugfs = debugfs_create_dir(rmem->name, debugfs_dir);
		swiotlb_create_debugfs_files(mem->debugfs);

			
}