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Date:   Thu, 11 Aug 2022 09:29:51 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Baoquan He <bhe@redhat.com>
Cc:     Michal Hocko <mhocko@suse.com>, Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        John Donnelly <john.p.donnelly@oracle.com>,
        David Hildenbrand <david@redhat.com>, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] dma/pool: do not complain if DMA pool is not allocated
Message-ID: <20220811072951.GC13886@lst.de>
References: <20220325122559.14251-1-mhocko@kernel.org> <Yj28gjonUa9+0yae@dhcp22.suse.cz> <20220325164856.GA16800@lst.de> <Yj3zyLs4f+ba6UqF@dhcp22.suse.cz> <YupFSpXOrcfXJNya@dhcp22.suse.cz> <YuqNToCACD8kKBG+@MiWiFi-R3L-srv> <YuqOrJKcgfamdXkk@dhcp22.suse.cz> <YuqU87SDwP0zg+c7@MiWiFi-R3L-srv>
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> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5aa4c2ecf5c7..93af781f9445 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2761,7 +2761,6 @@ config ISA_BUS
>  # x86_64 have no ISA slots, but can have ISA-style DMA.
>  config ISA_DMA_API
>  	bool "ISA-style DMA support" if (X86_64 && EXPERT)
> -	default y

This looks sensible to me, but you'll have to get it past Linus.

> -#ifdef CONFIG_ZONE_DMA
> +#if defined(CONFIG_ZONE_DMA) && defined(CONFIG_ISA_DMA_API)
>  	max_zone_pfns[ZONE_DMA]		= min(MAX_DMA_PFN, max_low_pfn);
> +#else
> +	max_zone_pfns[ZONE_DMA]		= min(MAX_DMA32_PFN, max_low_pfn);
>  #endif

But this simply can't work at all.