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Subject: Re: [PATCH v6] MIPS: Loongson: Add DMA support for LS7A
To:     Huacai Chen <chenhc@lemote.com>
References: <1588213867-32274-1-git-send-email-yangtiezhu@loongson.cn>
 <CAAhV-H5QBOnrqVbMfGf7H5vJ6UMhUxhkCqAzZiwRFn_VwTQHpA@mail.gmail.com>
Cc:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Christoph Hellwig <hch@infradead.org>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        "open list:MIPS" <linux-mips@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Xuefeng Li <lixuefeng@loongson.cn>
From:   Tiezhu Yang <yangtiezhu@loongson.cn>
Message-ID: <7d7f6211-f6bc-daae-5b13-b54092e762a1@loongson.cn>
Date:   Wed, 6 May 2020 14:38:16 +0800
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On 04/30/2020 02:19 PM, Huacai Chen wrote:
> Hi  Christoph,
>
> On Thu, Apr 30, 2020 at 10:31 AM 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.
> 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.

Thanks,
Tiezhu Yang

>
>> 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
>>
>> 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
>>