linux-kernel - Re: [PATCH 7/8] drm/loongson: Support to infer DC reversion from CPU's PRID value

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Message-ID: <CAA8EJpqrWV1f_pFqZt1Evo+WrZfy1mOynaTQ85uY9o4tVPZJPw@mail.gmail.com>
Date:   Mon, 30 Oct 2023 01:19:36 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Sui Jingfeng <suijingfeng@...ngson.cn>
Cc:     Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 7/8] drm/loongson: Support to infer DC reversion from
 CPU's PRID value

On Sun, 29 Oct 2023 at 21:46, Sui Jingfeng <suijingfeng@...ngson.cn> wrote:
>
> Due to the fact that the same display IP core has been integrated into
> different platform, there is a need to differentiate them on the runtime.
> The DC in LS7A1000/LS2K1000 has the PCI vendor & device ID of 0x0014:0x7A06
> The DC in LS7A2000/LS2K2000 has the PCI vendor & device ID of 0x0014:0x7A36
>
> Because the output ports and host platform of the DC IP varies, without a
> revision information we can't achieve fine-grained controls. The canonical
> approach to do such a thing is to read reversion register from the PCIe
> device. But LS2K1000 SoC was taped out at 2017, it is rather old. Our BIOS
> engineer don't assign a different revision ID to it, probably because of
> ignorance.
>
> LS2K2000 SoC was newly taped on 2023, we strictly force the BIOS engineer
> assign a different revision ID(0x10) to it. But the problem is that it is
> too casual, there is no formal convention or public documented rule
> established. For Loongson LS2K series SoC, the display controller IP is
> taped togather with the CPU core. For Loongson LS7A series bridge chips,
> the display controller IP is taped togather with the bridge chips itself.
> Consider the fact the all Loongson CPU has a unique PRID, this patch choose
> to infer DC reversion from CPU's PRID value.
>
>  - LS3A4000/LS3A5000 has 0xC0 as its processor ID.
>  - LS2K2000 has 0xB0 as its processor ID.
>  - LS2K2000LA has 0xA0 as its processor ID.
>
> The provided approach has no dependency on DT or ACPI, thus is preferfed.
> Besides, this approach can be used to acquire more addtional HW features.
> So the provided method has the potential to bring more benifits.
>
> Signed-off-by: Sui Jingfeng <suijingfeng@...ngson.cn>
> ---
>  drivers/gpu/drm/loongson/lsdc_drv.h   |  2 ++
>  drivers/gpu/drm/loongson/lsdc_probe.c | 35 +++++++++++++++++++++++++++
>  drivers/gpu/drm/loongson/lsdc_probe.h |  2 ++
>  3 files changed, 39 insertions(+)
>
> diff --git a/drivers/gpu/drm/loongson/lsdc_drv.h b/drivers/gpu/drm/loongson/lsdc_drv.h
> index 46ba9b88a30d..e1f4a2db2a0a 100644
> --- a/drivers/gpu/drm/loongson/lsdc_drv.h
> +++ b/drivers/gpu/drm/loongson/lsdc_drv.h
> @@ -42,6 +42,8 @@
>  enum loongson_chip_id {
>         CHIP_LS7A1000 = 0,
>         CHIP_LS7A2000 = 1,
> +       CHIP_LS2K1000 = 2,
> +       CHIP_LS2K2000 = 3,
>         CHIP_LS_LAST,
>  };
>
> diff --git a/drivers/gpu/drm/loongson/lsdc_probe.c b/drivers/gpu/drm/loongson/lsdc_probe.c
> index 48ba69bb8a98..f49b642d8f65 100644
> --- a/drivers/gpu/drm/loongson/lsdc_probe.c
> +++ b/drivers/gpu/drm/loongson/lsdc_probe.c
> @@ -54,3 +54,38 @@ unsigned int loongson_cpu_get_prid(u8 *imp, u8 *rev)
>
>         return prid;
>  }
> +
> +enum loongson_chip_id loongson_chip_id_fixup(enum loongson_chip_id chip_id)
> +{
> +       u8 impl;
> +
> +       if (loongson_cpu_get_prid(&impl, NULL)) {
> +               /*
> +                * LS2K2000 only has the LoongArch edition.
> +                */
> +               if (chip_id == CHIP_LS7A2000) {
> +                       if (impl == LOONGARCH_CPU_IMP_LS2K2000)
> +                               return CHIP_LS2K2000;
> +               }
> +
> +               /*
> +                * LS2K1000 has the LoongArch edition(with two LA264 CPU core)
> +                * and the Mips edition(with two mips64r2 CPU core), Only the
> +                * instruction set of the CPU are changed, the peripheral
> +                * devices are basically same.
> +                */
> +               if (chip_id == CHIP_LS7A1000) {
> +#if defined(__loongarch__)
> +                       if (impl == LOONGARCH_CPU_IMP_LS2K1000)
> +                               return CHIP_LS2K1000;
> +#endif
> +
> +#if defined(__mips__)
> +                       if (impl == LOONGSON_CPU_MIPS_IMP_LS2K)
> +                               return CHIP_LS2K1000;
> +#endif

Can you drop the ifdefs here? The code blocks do not seem to conflict
with each other.

> +               }
> +       }
> +
> +       return chip_id;
> +}
> diff --git a/drivers/gpu/drm/loongson/lsdc_probe.h b/drivers/gpu/drm/loongson/lsdc_probe.h
> index 8bb6de2e3c64..8c630c5c90ce 100644
> --- a/drivers/gpu/drm/loongson/lsdc_probe.h
> +++ b/drivers/gpu/drm/loongson/lsdc_probe.h
> @@ -9,4 +9,6 @@
>  /* Helpers for chip detection */
>  unsigned int loongson_cpu_get_prid(u8 *impl, u8 *rev);
>
> +enum loongson_chip_id loongson_chip_id_fixup(enum loongson_chip_id chip_id);
> +
>  #endif
> --
> 2.34.1
>


-- 
With best wishes
Dmitry