linux-kernel - Re: [PATCH v6] MIPS: Loongson: Add DMA support for LS7A

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Date:   Wed, 6 May 2020 16:47:30 +0800
From:   Huacai Chen <chenhc@...ote.com>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Christoph Hellwig <hch@...radead.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>
Subject: Re: [PATCH v6] MIPS: Loongson: Add DMA support for LS7A

Hi, Tiezhu,

On Wed, May 6, 2020 at 2:39 PM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>
> On 04/30/2020 02:19 PM, Huacai Chen wrote:
> > Hi  Christoph,
> >
> > On Thu, Apr 30, 2020 at 10:31 AM Tiezhu Yang <yangtiezhu@...ngson.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.
> > I know that you want use the default implementation of __phys_to_dma()
> > and __dma_to_phys() as more as possible. But, if that is "impossible"
> > on Loongson-3, should we still be forced to use the default? Yes, this
> > patch makes the default version work, but it limit the device's DMA
> > capability, which is not what we want.
>
> Hi Huacai,
>
> We know that the AMD RS780E bridge chip has been discontinued for
> some years, as time goes by, it will gradually quit the stage of
> history.
>
> Today and in the future, the most popular used bridge chip on the
> Loongson platform is LS7A, so the initial aim of this patch is to
> add DMA support for LS7A, at the same time, we should maintain
> downward compatibility for RS780E.
>
> For the above reasons, I think what you are concerned is not a
> big deal.
I don't think so, this is obviously a regression. If we can accept a
regression of RS780E, why we still maintain Loongson-2EF rather than
simply drop them?

>
> Thanks,
> Tiezhu Yang
>
> >
> >> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.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
> >>
> >> v6:
> >>    - make loongson_dma_config() static
> >>    - put ls7a things before rs780 things
> >>
> >>   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 f082d87..0c07a96 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 {
> >>          RS780E = 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 ls7a_dma_config(struct pci_dev *pdev);
> >> +extern void rs780e_dma_config(struct pci_dev *pdev);
> >> +
> >>   #endif
> >> diff --git a/arch/mips/loongson64/dma.c b/arch/mips/loongson64/dma.c
> >> index 5e86635..ef40b0d 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 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 = (paddr >> 44) & 0x3;
> >> -       return ((nid << 44) ^ paddr) | (nid << 37);
> >>   }
> >>
> >> -phys_addr_t __dma_to_phys(struct device *dev, dma_addr_t daddr)
> >> +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 = (daddr >> 37) & 0x3;
> >> -       return ((nid << 37) ^ daddr) | (nid << 44);
> >> +       pdev->dev.bus_dma_limit = DMA_BIT_MASK(36);
> >>   }
> >>
> >> +static 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
> >>
>