Messages in this thread | | | From | Arnd Bergmann <> | Date | Mon, 21 Mar 2022 18:07:39 +0100 | Subject | Re: [PATCH 4/9] soc: apple: Add SART driver |
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On Mon, Mar 21, 2022 at 5:50 PM Sven Peter <sven@svenpeter.dev> wrote: > > The NVMe co-processor on the Apple M1 uses a DMA address filter called > SART for some DMA transactions. This adds a simple driver used to > configure the memory regions from which DMA transactions are allowed. > > Co-developed-by: Hector Martin <marcan@marcan.st> > Signed-off-by: Hector Martin <marcan@marcan.st> > Signed-off-by: Sven Peter <sven@svenpeter.dev>
Can you add some explanation about why this uses a custom interface instead of hooking into the dma_map_ops?
> +static void sart2_get_entry(struct apple_sart *sart, int index, u8 *flags, > + phys_addr_t *paddr, size_t *size) > +{ > + u32 cfg = readl_relaxed(sart->regs + APPLE_SART2_CONFIG(index)); > + u32 paddr_ = readl_relaxed(sart->regs + APPLE_SART2_PADDR(index));
Why do you use the _relaxed() accessors here and elsewhere in the driver?
> +struct apple_sart *apple_sart_get(struct device *dev) > +{ > + struct device_node *sart_node; > + struct platform_device *sart_pdev; > + struct apple_sart *sart; > + > + sart_node = of_parse_phandle(dev->of_node, "apple,sart", 0); > + if (!sart_node) > + return ERR_PTR(ENODEV);
The error pointers need to take negative values, like 'ERR_PTR(-ENODEV)', here and everywhere else in the driver.
Arnd
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