linux-kernel - Re: [DO NOT MERGE v5 11/37] pci: pci-sh7751: Add SH7751 PCI driver

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Message-Id: <2ef81211-9525-4f96-a6b2-3fcfbed0c6e5@app.fastmail.com>
Date:   Tue, 05 Dec 2023 14:26:13 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Yoshinori Sato" <ysato@...rs.sourceforge.jp>,
        linux-sh@...r.kernel.org
Cc:     "Damien Le Moal" <dlemoal@...nel.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        "Conor Dooley" <conor+dt@...nel.org>,
        "Geert Uytterhoeven" <geert+renesas@...der.be>,
        "Michael Turquette" <mturquette@...libre.com>,
        "Stephen Boyd" <sboyd@...nel.org>,
        "Dave Airlie" <airlied@...il.com>,
        "Daniel Vetter" <daniel@...ll.ch>,
        "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>,
        "Maxime Ripard" <mripard@...nel.org>,
        "Thomas Zimmermann" <tzimmermann@...e.de>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Lorenzo Pieralisi" <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        "Bjorn Helgaas" <bhelgaas@...gle.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Jiri Slaby" <jirislaby@...nel.org>,
        "Magnus Damm" <magnus.damm@...il.com>,
        "Daniel Lezcano" <daniel.lezcano@...aro.org>,
        "Rich Felker" <dalias@...c.org>,
        "John Paul Adrian Glaubitz" <glaubitz@...sik.fu-berlin.de>,
        "Lee Jones" <lee@...nel.org>, "Helge Deller" <deller@....de>,
        Heiko Stübner <heiko@...ech.de>,
        "Jernej Skrabec" <jernej.skrabec@...il.com>,
        "Chris Morgan" <macromorgan@...mail.com>,
        "Linus Walleij" <linus.walleij@...aro.org>,
        "Randy Dunlap" <rdunlap@...radead.org>,
        "Hyeonggon Yoo" <42.hyeyoo@...il.com>,
        "David Rientjes" <rientjes@...gle.com>,
        "Vlastimil Babka" <vbabka@...e.cz>, "Baoquan He" <bhe@...hat.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Guenter Roeck" <linux@...ck-us.net>,
        "Stephen Rothwell" <sfr@...b.auug.org.au>,
        guoren <guoren@...nel.org>,
        "Javier Martinez Canillas" <javierm@...hat.com>,
        "Azeem Shaikh" <azeemshaikh38@...il.com>,
        "Palmer Dabbelt" <palmer@...osinc.com>,
        "Bin Meng" <bmeng@...ylab.org>,
        "Max Filippov" <jcmvbkbc@...il.com>, "Tom Rix" <trix@...hat.com>,
        "Herve Codina" <herve.codina@...tlin.com>,
        "Jacky Huang" <ychuang3@...oton.com>,
        "Lukas Bulwahn" <lukas.bulwahn@...il.com>,
        "Jonathan Corbet" <corbet@....net>,
        "Biju Das" <biju.das.jz@...renesas.com>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        "Sam Ravnborg" <sam@...nborg.org>,
        "Michael Karcher" <kernel@...rcher.dialup.fu-berlin.de>,
        "Sergey Shtylyov" <s.shtylyov@....ru>,
        "Laurent Pinchart" <laurent.pinchart+renesas@...asonboard.com>,
        linux-ide@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        linux-clk@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-pci@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-fbdev@...r.kernel.org
Subject: Re: [DO NOT MERGE v5 11/37] pci: pci-sh7751: Add SH7751 PCI driver

On Tue, Dec 5, 2023, at 10:45, Yoshinori Sato wrote:

> +#include <asm/addrspace.h>
> +#include "pci-sh7751.h"
> +
> +#define pcic_writel(val, base, reg) __raw_writel(val, base + (reg))
> +#define pcic_readl(base, reg) __raw_readl(base + (reg))

__raw_writel()/__raw_readl() has a number of problems with
atomicity (the compiler may split or merge pointer
dereferences), barriers and endianess. You should normally
always use readl()/writel() instead.

> +	memset(pci_config, 0, sizeof(pci_config));
> +	if (of_property_read_u32_array(np, "renesas,config",
> +				       pci_config, SH7751_NUM_CONFIG) == 0) {
> +		for (i = 0; i < SH7751_NUM_CONFIG; i++) {
> +			r = pci_config[i * 2];
> +			/* CONFIG0 is read-only, so make it a sentinel. */
> +			if (r == 0)
> +				break;
> +			pcic_writel(pci_config[i * 2 + 1], pcic, r * 4);
> +		}
> +	}

the config property seems a little too specific to this
implementation of the driver. Instead of encoding register
values in DT, I think these should either be described
in named properties where needed, or hardcoded in the driver
if there is only one sensible value.

> +/*
> + * We need to avoid collisions with `mirrored' VGA ports
> + * and other strange ISA hardware, so we always want the
> + * addresses to be allocated in the 0x000-0x0ff region
> + * modulo 0x400.
> + */
> +#define IO_REGION_BASE 0x1000
> +resource_size_t pcibios_align_resource(void *data, const struct 
> resource *res,
> +				resource_size_t size, resource_size_t align)
> +{

You can't have these generic functions in a driver, as that
prevents you from building more than one such driver.

The logic you have here is neither architecture nor
driver specific.

> +static int sh7751_pci_probe(struct platform_device *pdev)
> +{
> +	struct resource *res, *bscres;
> +	void __iomem *pcic;
> +	void __iomem *bsc;
> +	u32 memory[2];
> +	u16 vid, did;
> +	u32 word;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	if (IS_ERR(res))
> +		return PTR_ERR(res);
> +	pcic = (void __iomem *)res->start;

This cast is invalid, as res->start is a physical address
that you would need to ioremap() to turn into an __iomem
pointer.

> +	bscres = platform_get_resource(pdev, IORESOURCE_MEM, 1);
> +	bsc = devm_ioremap_resource(&pdev->dev, bscres);
> +	if (IS_ERR(bsc))
> +		return PTR_ERR(bsc);
> +
> +	if (of_property_read_u32_array(pdev->dev.of_node,
> +				       "renesas,memory", memory, 2) < 0) {
> +		/*
> +		 * If no memory range is specified,
> +		 *  the entire main memory will be targeted for DMA.
> +		 */
> +		memory[0] = memory_start;
> +		memory[1] = memory_end - memory_start;
> +	}

There is a generic "dma-ranges" proerty for describing
which memory is visible by a bus.

> diff --git a/drivers/pci/controller/pci-sh7751.h 
> b/drivers/pci/controller/pci-sh7751.h
> new file mode 100644
> index 000000000000..540cee7095c6
> --- /dev/null
> +++ b/drivers/pci/controller/pci-sh7751.h
> @@ -0,0 +1,76 @@

If the header is only included from one file, just removed
it and add the register definitions to the driver directly.

     Arnd