linux-kernel - Re: [PATCH/RFC 4/6] mm: Add NO

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Date:   Tue, 6 Feb 2018 12:47:56 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Arnd Bergmann <arnd@...db.de>, Mark Brown <broonie@...nel.org>,
        Richard Weinberger <richard@....at>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        iommu@...ts.linux-foundation.org, linux-usb@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH/RFC 4/6] mm: Add NO_DMA dummies for DMA pool API

Hi Geert,

On 06/02/18 10:14, Geert Uytterhoeven wrote:
> Add dummies for dma{,m}_pool_{create,destroy,alloc,free}(), to allow
> compile-testing if NO_DMA=y.
> 
> This prevents the following from showing up later:
> 
>      ERROR: "dma_pool_destroy" [drivers/usb/mtu3/mtu3.ko] undefined!
>      ERROR: "dma_pool_free" [drivers/usb/mtu3/mtu3.ko] undefined!
>      ERROR: "dma_pool_alloc" [drivers/usb/mtu3/mtu3.ko] undefined!
>      ERROR: "dma_pool_create" [drivers/usb/mtu3/mtu3.ko] undefined!
>      ERROR: "dma_pool_destroy" [drivers/scsi/hisi_sas/hisi_sas_main.ko] undefined!
>      ERROR: "dma_pool_free" [drivers/scsi/hisi_sas/hisi_sas_main.ko] undefined!
>      ERROR: "dma_pool_alloc" [drivers/scsi/hisi_sas/hisi_sas_main.ko] undefined!
>      ERROR: "dma_pool_create" [drivers/scsi/hisi_sas/hisi_sas_main.ko] undefined!
>      ERROR: "dma_pool_alloc" [drivers/mailbox/bcm-pdc-mailbox.ko] undefined!
>      ERROR: "dma_pool_free" [drivers/mailbox/bcm-pdc-mailbox.ko] undefined!
>      ERROR: "dma_pool_create" [drivers/mailbox/bcm-pdc-mailbox.ko] undefined!
>      ERROR: "dma_pool_destroy" [drivers/mailbox/bcm-pdc-mailbox.ko] undefined!
> 
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
>   include/linux/dmapool.h | 21 +++++++++++++++++++--
>   1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/dmapool.h b/include/linux/dmapool.h
> index 53ba737505df31c7..adeb5e56c3ad73a8 100644
> --- a/include/linux/dmapool.h
> +++ b/include/linux/dmapool.h
> @@ -16,6 +16,7 @@
>   
>   struct device;
>   
> +#ifdef CONFIG_HAS_DMA
>   struct dma_pool *dma_pool_create(const char *name, struct device *dev,
>   			size_t size, size_t align, size_t allocation);
>   
> @@ -23,6 +24,17 @@ void dma_pool_destroy(struct dma_pool *pool);
>   
>   void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
>   		     dma_addr_t *handle);
> +void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t addr);
> +#else /* !CONFIG_HAS_DMA */
> +static inline struct dma_pool *dma_pool_create(const char *name,
> +	struct device *dev, size_t size, size_t align, size_t allocation)
> +{ return NULL; }
> +static inline void dma_pool_destroy(struct dma_pool *pool) { }
> +static inline void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
> +				   dma_addr_t *handle) { return NULL; }
> +static inline void dma_pool_free(struct dma_pool *pool, void *vaddr,
> +				 dma_addr_t addr) { }
> +#endif /* !CONFIG_HAS_DMA */
>   
>   static inline void *dma_pool_zalloc(struct dma_pool *pool, gfp_t mem_flags,
>   				    dma_addr_t *handle)
> @@ -30,14 +42,19 @@ static inline void *dma_pool_zalloc(struct dma_pool *pool, gfp_t mem_flags,
>   	return dma_pool_alloc(pool, mem_flags | __GFP_ZERO, handle);
>   }
>   
> -void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t addr);
> -
>   /*
>    * Managed DMA pool
>    */
> +#ifdef CONFIG_HAS_DMA
>   struct dma_pool *dmam_pool_create(const char *name, struct device *dev,
>   				  size_t size, size_t align, size_t allocation);
>   void dmam_pool_destroy(struct dma_pool *pool);
> +#else /* !CONFIG_HAS_DMA */
> +static inline struct dma_pool *dmam_pool_create(const char *name,
> +	struct device *dev, size_t size, size_t align, size_t allocation)
> +{ return NULL; }
> +static inline void dmam_pool_destroy(struct dma_pool *pool) { }
> +#endif /* !CONFIG_HAS_DMA */

Nit: It might be tidier to add *all* the stubs down here so that there 
only need be a single #ifdef, then move the dma_pool_zalloc definition 
outside at the end (where we might eventually get rid of it anyway).

Other than that, though, I think I agree with the series in general - 
more COMPILE_TEST is always good from the point of view of weeding out 
drivers using architecture-specific DMA API internals which aren't part 
of the proper generic interface.

Robin.

>   
>   #endif
>   
>