From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755915AbeEaRZG (ORCPT ); Thu, 31 May 2018 13:25:06 -0400 Received: from foss.arm.com ([217.140.101.70]:44052 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755721AbeEaRZE (ORCPT ); Thu, 31 May 2018 13:25:04 -0400 Subject: Re: [PATCH 1/2] dma-coherent: Add one parameter to save available coherent memory To: Baolin Wang , hch@lst.de, m.szyprowski@samsung.com Cc: gregkh@linuxfoundation.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, arnd@arndb.de, broonie@kernel.org References: From: Robin Murphy Message-ID: <1d02b2e1-dd1c-af2a-e980-29aef4aa0c00@arm.com> Date: Thu, 31 May 2018 18:25:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 31/05/18 06:55, Baolin Wang wrote: > It is incorrect to use mem->size to valid if there are enough coherent > memory to allocate in __dma_alloc_from_coherent(), since some devices > may mark some occupied coherent memory by dma_mark_declared_memory_occupied(). > > So we can introduce one 'avail' parameter to save the available device > coherent memory, to valid if we have enough coherent memory for the device > to allocate. We already have dma_mem->size stored for other reasons, so there's little harm in using it for a rough sanity check to short-circuit the odd allocation which cannot possibly succeed, but adding machinery purely for the sake an ever-so-slightly more accurate, but still far from exhaustive, check doesn't really seem worth it. Even if size <= dma_mem->avail there's still no guarantee that the allocation will actually succeed, so what benefit does the explicit accounting provide? Robin. > Signed-off-by: Baolin Wang > --- > drivers/base/dma-coherent.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c > index 597d408..ce19832 100644 > --- a/drivers/base/dma-coherent.c > +++ b/drivers/base/dma-coherent.c > @@ -18,6 +18,7 @@ struct dma_coherent_mem { > unsigned long *bitmap; > spinlock_t spinlock; > bool use_dev_dma_pfn_offset; > + int avail; > }; > > static struct dma_coherent_mem *dma_coherent_default_memory __ro_after_init; > @@ -73,6 +74,7 @@ static int dma_init_coherent_memory( > dma_mem->device_base = device_addr; > dma_mem->pfn_base = PFN_DOWN(phys_addr); > dma_mem->size = pages; > + dma_mem->avail = pages; > dma_mem->flags = flags; > spin_lock_init(&dma_mem->spinlock); > > @@ -141,6 +143,7 @@ void *dma_mark_declared_memory_occupied(struct device *dev, > dma_addr_t device_addr, size_t size) > { > struct dma_coherent_mem *mem = dev->dma_mem; > + int order = get_order(size); > unsigned long flags; > int pos, err; > > @@ -151,7 +154,9 @@ void *dma_mark_declared_memory_occupied(struct device *dev, > > spin_lock_irqsave(&mem->spinlock, flags); > pos = PFN_DOWN(device_addr - dma_get_device_base(dev, mem)); > - err = bitmap_allocate_region(mem->bitmap, pos, get_order(size)); > + err = bitmap_allocate_region(mem->bitmap, pos, order); > + if (!err) > + mem->avail -= 1 << order; > spin_unlock_irqrestore(&mem->spinlock, flags); > > if (err != 0) > @@ -170,7 +175,7 @@ static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem, > > spin_lock_irqsave(&mem->spinlock, flags); > > - if (unlikely(size > (mem->size << PAGE_SHIFT))) > + if (unlikely(size > (mem->avail << PAGE_SHIFT))) > goto err; > > pageno = bitmap_find_free_region(mem->bitmap, mem->size, order); > @@ -182,6 +187,7 @@ static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem, > */ > *dma_handle = mem->device_base + (pageno << PAGE_SHIFT); > ret = mem->virt_base + (pageno << PAGE_SHIFT); > + mem->avail -= 1 << order; > spin_unlock_irqrestore(&mem->spinlock, flags); > memset(ret, 0, size); > return ret; > @@ -244,6 +250,7 @@ static int __dma_release_from_coherent(struct dma_coherent_mem *mem, > > spin_lock_irqsave(&mem->spinlock, flags); > bitmap_release_region(mem->bitmap, page, order); > + mem->avail += 1 << order; > spin_unlock_irqrestore(&mem->spinlock, flags); > return 1; > } >