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Date: Mon, 12 Aug 2013 10:59:57 +0900
From: Cho KyongHo <pullip.cho@...sung.com>
To: Tomasz Figa <t.figa@...sung.com>
Cc: Tomasz Figa <tomasz.figa@...il.com>,
'Linux ARM Kernel' <linux-arm-kernel@...ts.infradead.org>,
'Linux IOMMU' <iommu@...ts.linux-foundation.org>,
'Linux Kernel' <linux-kernel@...r.kernel.org>,
'Linux Samsung SOC' <linux-samsung-soc@...r.kernel.org>,
devicetree@...r.kernel.org, 'Joerg Roedel' <joro@...tes.org>,
'Kukjin Kim' <kgene.kim@...sung.com>,
'Prathyush' <prathyush.k@...sung.com>,
'Rahul Sharma' <rahul.sharma@...sung.com>,
'Subash Patel' <supash.ramaswamy@...aro.org>,
'Grant Grundler' <grundler@...omium.org>,
'Antonios Motakis' <a.motakis@...tualopensystems.com>,
kvmarm@...ts.cs.columbia.edu,
'Sachin Kamat' <sachin.kamat@...aro.org>
Subject: Re: [PATCH v9 04/16] iommu/exynos: allocate lv2 page table from own
slab
On Fri, 09 Aug 2013 11:35:20 +0200, Tomasz Figa wrote:
> On Friday 09 of August 2013 17:51:56 Cho KyongHo wrote:
> > On Fri, 09 Aug 2013 09:55:30 +0200, Tomasz Figa wrote:
> > > Hi KyongHo,
> > >
> > > On Friday 09 of August 2013 14:58:49 Cho KyongHo wrote:
> > > > On Thu, 08 Aug 2013 16:00:18 +0200, Tomasz Figa wrote:
> > > > > On Thursday 08 of August 2013 18:38:04 Cho KyongHo wrote:
> > > > > > Since kmalloc() does not guarantee that the allignment of 1KiB
> > > > > > when
> > > > > > it
> > > > > > allocates 1KiB, it is required to allocate lv2 page table from
> > > > > > own
> > > > > > slab that guarantees alignment of 1KiB
> > > > > >
> > > > > > Signed-off-by: Cho KyongHo <pullip.cho@...sung.com>
> > > > > > ---
> > > > > >
> > > > > > drivers/iommu/exynos-iommu.c | 24 ++++++++++++++++++++----
> > > > > > 1 files changed, 20 insertions(+), 4 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/iommu/exynos-iommu.c
> > > > > > b/drivers/iommu/exynos-iommu.c index d90e6fa..a318049 100644
> > > > > > --- a/drivers/iommu/exynos-iommu.c
> > > > > > +++ b/drivers/iommu/exynos-iommu.c
> > > > > > @@ -100,6 +100,8 @@
> > > > > >
> > > > > > #define REG_PB1_SADDR 0x054
> > > > > > #define REG_PB1_EADDR 0x058
> > > > > >
> > > > > > +static struct kmem_cache *lv2table_kmem_cache;
> > > > > > +
> > > > > >
> > > > > > static unsigned long *section_entry(unsigned long *pgtable,
> > > > > > unsigned
> > > > > >
> > > > > > long iova) {
> > > > > >
> > > > > > return pgtable + lv1ent_offset(iova);
> > > > > >
> > > > > > @@ -765,7 +767,8 @@ static void
> > > > > > exynos_iommu_domain_destroy(struct
> > > > > > iommu_domain *domain)
> > > > > >
> > > > > > for (i = 0; i < NUM_LV1ENTRIES; i++)
> > > > > >
> > > > > > if (lv1ent_page(priv->pgtable + i))
> > > > > >
> > > > > > - kfree(__va(lv2table_base(priv->pgtable + i)));
> > > > > > + kmem_cache_free(lv2table_kmem_cache,
> > > > > > + __va(lv2table_base(priv->pgtable +
> > >
> > > i)));
> > >
> > > > > > free_pages((unsigned long)priv->pgtable, 2);
> > > > > > free_pages((unsigned long)priv->lv2entcnt, 1);
> > > > > >
> > > > > > @@ -861,7 +864,7 @@ static unsigned long *alloc_lv2entry(unsigned
> > > > > > long
> > > > > > *sent, unsigned long iova, if (lv1ent_fault(sent)) {
> > > > > >
> > > > > > unsigned long *pent;
> > > > > >
> > > > > > - pent = kzalloc(LV2TABLE_SIZE, GFP_ATOMIC);
> > > > > > + pent = kmem_cache_zalloc(lv2table_kmem_cache, GFP_ATOMIC);
> > > > > >
> > > > > > BUG_ON((unsigned long)pent & (LV2TABLE_SIZE - 1));
> > > > > > if (!pent)
> > > > > >
> > > > > > return ERR_PTR(-ENOMEM);
> > > > > >
> > > > > > @@ -881,7 +884,7 @@ static int lv1set_section(unsigned long
> > > > > > *sent,
> > > > > > phys_addr_t paddr, short *pgcnt)
> > > > > >
> > > > > > if (lv1ent_page(sent)) {
> > > > > >
> > > > > > BUG_ON(*pgcnt != NUM_LV2ENTRIES);
> > > > > >
> > > > > > - kfree(page_entry(sent, 0));
> > > > > > + kmem_cache_free(lv2table_kmem_cache, page_entry(sent, 0));
> > > > > >
> > > > > > *pgcnt = 0;
> > > > > >
> > > > > > }
> > > > > >
> > > > > > @@ -1082,10 +1085,23 @@ static int __init exynos_iommu_init(void)
> > > > > >
> > > > > > {
> > > > > >
> > > > > > int ret;
> > > > > >
> > > > > > + lv2table_kmem_cache =
> > > > > > kmem_cache_create("exynos-iommu-lv2table",
> > > > > > + LV2TABLE_SIZE, LV2TABLE_SIZE, 0, NULL);
> > > > > > + if (!lv2table_kmem_cache) {
> > > > > > + pr_err("%s: Failed to create kmem cache\n", __func__);
> > > > > > + return -ENOMEM;
> > > > > > + }
> > > > > > +
> > > > > >
> > > > > > ret = platform_driver_register(&exynos_sysmmu_driver);
> > > > > >
> > > > > > if (ret == 0)
> > > > > >
> > > > > > - bus_set_iommu(&platform_bus_type, &exynos_iommu_ops);
> > > > > > + ret = bus_set_iommu(&platform_bus_type,
> > >
> > > &exynos_iommu_ops);
> > >
> > > > > > +
> > > > > > + if (ret) {
> > > > > > + pr_err("%s: Failed to register exynos-iommu driver.\n",
> > > > > > + __func__);
> > > > > > + kmem_cache_destroy(lv2table_kmem_cache);
> > > > > > + }
> > > > >
> > > > > What about making the return value handling here cleaner? For
> example:
> > > > > lv2table_kmem_cache = kmem_cache_create("exynos-iommu-lv2table",
> > > > >
> > > > > LV2TABLE_SIZE, LV2TABLE_SIZE, 0, NULL);
> > > > >
> > > > > if (!lv2table_kmem_cache) {
> > > > >
> > > > > ...
> > > > > return -ENOMEM;
> > > > >
> > > > > }
> > > > >
> > > > > ret = platform_driver_register(&exynos_sysmmu_driver);
> > > > > if (ret) {
> > > > >
> > > > > ...
> > > > > goto err_destroy_kmem_cache;
> > > > >
> > > > > }
> > > > >
> > > > > ret = bus_set_iommu(&platform_bus_type, &exynos_iommu_ops);
> > > > > if (ret) {
> > > > >
> > > > > ...
> > > > > goto err_platform_unregister;
> > > > >
> > > > > }
> > > > >
> > > > > return 0;
> > > > >
> > > > > err_platform_unregister:
> > > > > ...
> > > > >
> > > > > err_destroy_kmem_cache:
> > > > > ...
> > > > > return ret;
> > > > >
> > > > > }
> > > >
> > > > Thank you for suggestion.
> > > > I think you are worrying about missing the information who makes
> > > > 'ret'
> > > > non-zero.
> > >
> > > Oh, this is a valid point, but it was more a nitpick about the coding
> > > style. Single path error handling (with goto) is widely used in the
> > > kernel in cases when more than one thing has to be undone and so I
> > > suggested this method of error handling here as well.
> > >
> > > > Ok. I will process it separately.
> > >
> > > Since this patch adds most of the error handling to this function, I
> > > think it should be fine to do it as a part of this patch.
> >
> > I meant 'separately' that checking all return values each.
> > I think it can be simpler without goto.
> >
> > There are just 2 cases to rollback previous changes in that function.
>
> It might end up with less lines, but having roll back in single place is
> more readable. That's why it's the preferred error handling way in Linux
> kernel, if you have more than one action to undo on your error path.
>
I fully understand what you are concerning about and I also agree.
Actually it is simple choice without any side effect.
It is just a preference.
I will change it into 'goto'.
Then we can determine what looks better :)
Thank you.
KyongHo.
> Best regards,
> Tomasz
>
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