Re: [PATCH v5] MIPS: Loongson: Add DMA support for LS7A

[Huacai Chen <chenhc@lemote.com>]

Hi, Tiezhu,

On Wed, Apr 29, 2020 at 3:00 PM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>
> In the current market, the most used bridge chip on the Loongson
> platform are RS780E and LS7A, the RS780E bridge chip is already
> supported by the mainline kernel.
>
> In order to use the default implementation of __phys_to_dma() and
> __dma_to_phys() in dma-direct.h, remove CONFIG_ARCH_HAS_PHYS_TO_DMA
> and then set the bus's DMA limit to 36 bit for RS780E to maintain
> downward compatibility.
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---
>
> Hi Christoph and Jiaxun,
>
> Thank you very much for your suggestions.
>
> v5:
>   - use the default implementation of __phys_to_dma()
>     and __dma_to_phys() in dma-direct.h
>
>  arch/mips/Kconfig                                  |  1 -
>  arch/mips/include/asm/mach-loongson64/boot_param.h |  5 +++++
>  arch/mips/loongson64/dma.c                         | 22 +++++++++++-----------
>  arch/mips/loongson64/env.c                         |  2 ++
>  4 files changed, 18 insertions(+), 12 deletions(-)
>
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 9f15539..12b6bdb 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -1454,7 +1454,6 @@ choice
>  config CPU_LOONGSON64
>         bool "Loongson 64-bit CPU"
>         depends on SYS_HAS_CPU_LOONGSON64
> -       select ARCH_HAS_PHYS_TO_DMA
>         select CPU_MIPSR2
>         select CPU_HAS_PREFETCH
>         select CPU_SUPPORTS_64BIT_KERNEL
> diff --git a/arch/mips/include/asm/mach-loongson64/boot_param.h b/arch/mips/include/asm/mach-loongson64/boot_param.h
> index fc9f14b..cccf4cb 100644
> --- a/arch/mips/include/asm/mach-loongson64/boot_param.h
> +++ b/arch/mips/include/asm/mach-loongson64/boot_param.h
> @@ -197,6 +197,7 @@ enum loongson_bridge_type {
>         LS7A = 2
>  };
>
> +struct pci_dev;
>  struct loongson_system_configuration {
>         u32 nr_cpus;
>         u32 nr_nodes;
> @@ -221,9 +222,13 @@ struct loongson_system_configuration {
>         u32 nr_sensors;
>         struct sensor_device sensors[MAX_SENSORS];
>         u64 workarounds;
> +       void (*dma_config)(struct pci_dev *pdev);
>  };
>
>  extern struct efi_memory_map_loongson *loongson_memmap;
>  extern struct loongson_system_configuration loongson_sysconf;
>
> +extern void rs780e_dma_config(struct pci_dev *pdev);
> +extern void ls7a_dma_config(struct pci_dev *pdev);
Please use alpha-betical order here, which means put ls7a things
before rs780 things.

> +
>  #endif
> diff --git a/arch/mips/loongson64/dma.c b/arch/mips/loongson64/dma.c
> index 5e86635..6878bcc 100644
> --- a/arch/mips/loongson64/dma.c
> +++ b/arch/mips/loongson64/dma.c
> @@ -1,24 +1,24 @@
>  // SPDX-License-Identifier: GPL-2.0
> -#include <linux/dma-direct.h>
> +#include <linux/pci.h>
>  #include <linux/init.h>
>  #include <linux/swiotlb.h>
>
> -dma_addr_t __phys_to_dma(struct device *dev, phys_addr_t paddr)
> +void rs780e_dma_config(struct pci_dev *pdev)
>  {
> -       /* We extract 2bit node id (bit 44~47, only bit 44~45 used now) from
> -        * Loongson-3's 48bit address space and embed it into 40bit */
> -       long nid = (paddr >> 44) & 0x3;
> -       return ((nid << 44) ^ paddr) | (nid << 37);
> +       pdev->dev.bus_dma_limit = DMA_BIT_MASK(36);
>  }
>
> -phys_addr_t __dma_to_phys(struct device *dev, dma_addr_t daddr)
> +void ls7a_dma_config(struct pci_dev *pdev)
>  {
> -       /* We extract 2bit node id (bit 44~47, only bit 44~45 used now) from
> -        * Loongson-3's 48bit address space and embed it into 40bit */
> -       long nid = (daddr >> 37) & 0x3;
> -       return ((nid << 37) ^ daddr) | (nid << 44);
>  }
Why use a hardcoded 37? LS7A's node-id bits are configurable in BIOS.

>
> +void loongson_dma_config(struct pci_dev *pdev)
> +{
> +       loongson_sysconf.dma_config(pdev);
> +}
> +
> +DECLARE_PCI_FIXUP_EARLY(PCI_ANY_ID, PCI_ANY_ID, loongson_dma_config);
> +
>  void __init plat_swiotlb_setup(void)
>  {
>         swiotlb_init(1);
> diff --git a/arch/mips/loongson64/env.c b/arch/mips/loongson64/env.c
> index 71f4aaf..496f401 100644
> --- a/arch/mips/loongson64/env.c
> +++ b/arch/mips/loongson64/env.c
> @@ -192,8 +192,10 @@ void __init prom_init_env(void)
>         if (vendor == PCI_VENDOR_ID_LOONGSON && device == 0x7a00) {
>                 pr_info("The bridge chip is LS7A\n");
>                 loongson_sysconf.bridgetype = LS7A;
> +               loongson_sysconf.dma_config = ls7a_dma_config;
>         } else {
>                 pr_info("The bridge chip is RS780E or SR5690\n");
>                 loongson_sysconf.bridgetype = RS780E;
> +               loongson_sysconf.dma_config = rs780e_dma_config;
>         }
>  }
> --
> 2.1.0
>