linux-kernel - Re: [PATCH v2 2/5] MIPS: ralink: implement 'pcibios_root_bridge

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Message-ID: <6ebd3d77-e012-4b27-f0dc-a81c59d76fe4@roeck-us.net>
Date:   Thu, 2 Dec 2021 11:45:09 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Sergio Paracuellos <sergio.paracuellos@...il.com>,
        linux-pci@...r.kernel.org
Cc:     linux-mips@...r.kernel.org, tsbogend@...ha.franken.de,
        lorenzo.pieralisi@....com, bhelgaas@...gle.com, arnd@...db.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/5] MIPS: ralink: implement
 'pcibios_root_bridge_prepare()'

On 12/1/21 1:51 PM, Sergio Paracuellos wrote:
> PCI core code call 'pcibios_root_bridge_prepare()' function inside function
> 'pci_register_host_bridge()'. This point is very good way to properly enter
> into this MIPS ralink specific code to properly setup I/O coherency units
> with PCI memory addresses.
> 
> Signed-off-by: Sergio Paracuellos <sergio.paracuellos@...il.com>
> ---
>   arch/mips/ralink/mt7621.c | 30 ++++++++++++++++++++++++++++++
>   1 file changed, 30 insertions(+)
> 
> diff --git a/arch/mips/ralink/mt7621.c b/arch/mips/ralink/mt7621.c
> index bd71f5b14238..7649416c1cd7 100644
> --- a/arch/mips/ralink/mt7621.c
> +++ b/arch/mips/ralink/mt7621.c
> @@ -10,6 +10,7 @@
>   #include <linux/slab.h>
>   #include <linux/sys_soc.h>
>   #include <linux/memblock.h>
> +#include <linux/pci.h>
>   
>   #include <asm/bootinfo.h>
>   #include <asm/mipsregs.h>
> @@ -22,6 +23,35 @@
>   
>   static void *detect_magic __initdata = detect_memory_region;
>   
> +int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
> +{
> +	struct resource_entry *entry;
> +	resource_size_t mask;
> +
> +	entry = resource_list_first_type(&bridge->windows, IORESOURCE_MEM);
> +	if (!entry) {
> +		pr_err("Cannot get memory resource\n");
> +		return -EINVAL;
> +	}
> +
> +	if (mips_cps_numiocu(0)) {
> +		/*
> +		 * FIXME: hardware doesn't accept mask values with 1s after
> +		 * 0s (e.g. 0xffef), so it would be great to warn if that's
> +		 * about to happen
> +		 */
> +		mask = ~(entry->res->end - entry->res->start);
> +

One more comment: From the include file,

#define CM_GCR_REGn_MASK_ADDRMASK               GENMASK(31, 16)

suggests that only the upper 16 bit are valid (relevant ?) for the mask.
Given that, it might make sense to make sure that the lower 16 bit are not set,
maybe with
		mask = ~(entry->res->end - entry->res->start) & CM_GCR_REGn_MASK_ADDRMASK;

Thanks,
Guenter

> +		write_gcr_reg1_base(entry->res->start);
> +		write_gcr_reg1_mask(mask | CM_GCR_REGn_MASK_CMTGT_IOCU0);
> +		pr_info("PCI coherence region base: 0x%08llx, mask/settings: 0x%08llx\n",
> +			(unsigned long long)read_gcr_reg1_base(),
> +			(unsigned long long)read_gcr_reg1_mask());
> +	}
> +
> +	return 0;
> +}
> +
>   phys_addr_t mips_cpc_default_phys_base(void)
>   {
>   	panic("Cannot detect cpc address");
>