linux-kernel - Re: [PATCH 1/1] powerpc/kernel/iommu: Use largepool as a last resort when !largealloc

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Date:   Thu, 22 Apr 2021 03:50:44 -0300
From:   Leonardo Bras <leobras.c@...il.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Nicolin Chen <nicoleotsuka@...il.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] powerpc/kernel/iommu: Use largepool as a last
 resort when !largealloc

Hello,

FYI: This patch was reviewed when it was part of another patchset:
http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20200817234033.442511-4-leobras.c@gmail.com/


On Thu, 2021-03-18 at 14:44 -0300, Leonardo Bras wrote:
> As of today, doing iommu_range_alloc() only for !largealloc (npages <= 15)
> will only be able to use 3/4 of the available pages, given pages on
> largepool  not being available for !largealloc.
> 
> This could mean some drivers not being able to fully use all the available
> pages for the DMA window.
> 
> Add pages on largepool as a last resort for !largealloc, making all pages
> of the DMA window available.
> 
> Signed-off-by: Leonardo Bras <leobras.c@...il.com>
> Reviewed-by: Alexey Kardashevskiy <aik@...abs.ru>
> ---
>  arch/powerpc/kernel/iommu.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
> index 3329ef045805..ae6ad8dca605 100644
> --- a/arch/powerpc/kernel/iommu.c
> +++ b/arch/powerpc/kernel/iommu.c
> @@ -255,6 +255,15 @@ static unsigned long iommu_range_alloc(struct device *dev,
>  			pass++;
>  			goto again;
>  
> 
> +		} else if (pass == tbl->nr_pools + 1) {
> +			/* Last resort: try largepool */
> +			spin_unlock(&pool->lock);
> +			pool = &tbl->large_pool;
> +			spin_lock(&pool->lock);
> +			pool->hint = pool->start;
> +			pass++;
> +			goto again;
> +
>  		} else {
>  			/* Give up */
>  			spin_unlock_irqrestore(&(pool->lock), flags);