[{"id":3675131,"web_url":"http://patchwork.ozlabs.org/comment/3675131/","msgid":"","list_archive_url":null,"date":"2026-04-09T07:53:55","subject":"Re: [RFC PATCH 1/5] gpio: generic: add a generic register wrapper for\n MMIO and PMIO","submitter":{"id":92050,"url":"http://patchwork.ozlabs.org/api/people/92050/","name":"Linus Walleij","email":"linusw@kernel.org"},"content":"Hi Jose,\n\nthanks for your patch!\n\nOn Tue, Apr 7, 2026 at 8:49 PM Jose Javier Rodriguez Barbarin\n wrote:\n\n> For adding support to port-mapped devices within gpio_generic_chip, a new\n> data type is required for passing to read_reg() and write_reg()\n> callbacks as I/O port-mapped and memory-mapped registers use different\n> data types.\n>\n> Introduce a new struct gpio_chip_reg to encapsulate mmio addresses and\n> I/O port numbers.\n>\n> Signed-off-by: Jose Javier Rodriguez Barbarin \n\nOverall this is just fine, but I have one idea:\n\n> +struct gpio_chip_reg {\n> + void __iomem *mmio;\n> + unsigned long port;\n> +};\n\nSince you're always using one or the other, can we use a union?\n\nunion gpio_chip_reg {\n void __iomem *mmio;\n unsigned long port;\n};\n\nThis way it will use the same amount of memory no matter which version is\nused.\n\nOK it's a micro-optimization but also elegant because it reflects the fact that\nwe just use one or the other.\n\nYours,\nLinus Walleij","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linux-gpio@vger.kernel.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256\n header.s=k20201202 header.b=cI32OPlg;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org\n (client-ip=2600:3c04:e001:36c::12fc:5321; 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