[PATCH] Revert "dma-contiguous: do not allocate a single page from CMA area"

[PATCH] Revert "dma-contiguous: do not allocate a single page from CMA area"

[Nicolin Chen]

This reverts commit d222e42e88168fd67e6d131984b86477af1fc256.

The original change breaks omap dss:
    omapdss_dispc 58001000.dispc:
        dispc_errata_i734_wa_init: dma_alloc_writecombine failed

Let's revert it first and then find a safer solution instead.

Reported-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
---
Tony,
	
Would you please test and verify? Thanks!

 kernel/dma/contiguous.c | 22 +++-------------------
 1 file changed, 3 insertions(+), 19 deletions(-)

diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 09074bd04793..b2a87905846d 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -186,32 +186,16 @@ int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base,
  *
  * This function allocates memory buffer for specified device. It uses
  * device specific contiguous memory area if available or the default
- * global one.
- *
- * However, it skips one-page size of allocations from the global area.
- * As the addresses within one page are always contiguous, so there is
- * no need to waste CMA pages for that kind; it also helps reduce the
- * fragmentations in the CMA area. So a caller should be the rebounder
- * in such case to allocate a normal page upon NULL return value.
- *
- * Requires architecture specific dev_get_cma_area() helper function.
+ * global one. Requires architecture specific dev_get_cma_area() helper
+ * function.
  */
 struct page *dma_alloc_from_contiguous(struct device *dev, size_t count,
 				       unsigned int align, bool no_warn)
 {
-	struct cma *cma;
-
 	if (align > CONFIG_CMA_ALIGNMENT)
 		align = CONFIG_CMA_ALIGNMENT;
 
-	if (dev && dev->cma_area)
-		cma = dev->cma_area;
-	else if (count > 1)
-		cma = dma_contiguous_default_area;
-	else
-		return NULL;
-
-	return cma_alloc(cma, count, align, no_warn);
+	return cma_alloc(dev_get_cma_area(dev), count, align, no_warn);
 }
 
 /**
-- 
2.17.1

Re: [PATCH] Revert "dma-contiguous: do not allocate a single page from CMA area"

[Robin Murphy]

On 2019-02-26 8:23 pm, Nicolin Chen wrote:
> This reverts commit d222e42e88168fd67e6d131984b86477af1fc256.
> 
> The original change breaks omap dss:
>      omapdss_dispc 58001000.dispc:
>          dispc_errata_i734_wa_init: dma_alloc_writecombine failed
> 
> Let's revert it first and then find a safer solution instead.

Ah, I think I see the problem - once arch/arm's __dma_alloc() has 
decided to use CMA (because dev_get_cma_area(dev) returns the global 
area), it then won't fall back to trying a regular page allocation if 
dma_alloc_from_contiguous() returns NULL. Thus anything on 32-bit Arm 
trying to allocate a single-page buffer in blockable context with a 
CMA-enabled config is just going to fail. Similarly, it looks like none 
of the DMA_ATTR_FORCE_CONTIGUOUS cases are prepared to handle this 
change either (amd_iommu appears technically affected, but is already 
using dma_alloc_from_contiguous() backwards compared to everyone else, hmm).

I guess the question is whether to add alloc_page()/free_page() 
fallbacks to those call sites, or stuff them directly into the CMA 
helpers here.

Robin.

> Reported-by: Tony Lindgren <tony@atomide.com>
> Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
> ---
> Tony,
> 	
> Would you please test and verify? Thanks!
> 
>   kernel/dma/contiguous.c | 22 +++-------------------
>   1 file changed, 3 insertions(+), 19 deletions(-)
> 
> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> index 09074bd04793..b2a87905846d 100644
> --- a/kernel/dma/contiguous.c
> +++ b/kernel/dma/contiguous.c
> @@ -186,32 +186,16 @@ int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base,
>    *
>    * This function allocates memory buffer for specified device. It uses
>    * device specific contiguous memory area if available or the default
> - * global one.
> - *
> - * However, it skips one-page size of allocations from the global area.
> - * As the addresses within one page are always contiguous, so there is
> - * no need to waste CMA pages for that kind; it also helps reduce the
> - * fragmentations in the CMA area. So a caller should be the rebounder
> - * in such case to allocate a normal page upon NULL return value.
> - *
> - * Requires architecture specific dev_get_cma_area() helper function.
> + * global one. Requires architecture specific dev_get_cma_area() helper
> + * function.
>    */
>   struct page *dma_alloc_from_contiguous(struct device *dev, size_t count,
>   				       unsigned int align, bool no_warn)
>   {
> -	struct cma *cma;
> -
>   	if (align > CONFIG_CMA_ALIGNMENT)
>   		align = CONFIG_CMA_ALIGNMENT;
>   
> -	if (dev && dev->cma_area)
> -		cma = dev->cma_area;
> -	else if (count > 1)
> -		cma = dma_contiguous_default_area;
> -	else
> -		return NULL;
> -
> -	return cma_alloc(cma, count, align, no_warn);
> +	return cma_alloc(dev_get_cma_area(dev), count, align, no_warn);
>   }
>   
>   /**
> 

Re: [PATCH] Revert "dma-contiguous: do not allocate a single page from CMA area"

[Tony Lindgren]

* Robin Murphy <robin.murphy@arm.com> [190226 23:36]:
> On 2019-02-26 8:23 pm, Nicolin Chen wrote:
> > This reverts commit d222e42e88168fd67e6d131984b86477af1fc256.
> > 
> > The original change breaks omap dss:
> >      omapdss_dispc 58001000.dispc:
> >          dispc_errata_i734_wa_init: dma_alloc_writecombine failed
> > 
> > Let's revert it first and then find a safer solution instead.

Sounds like a good idea since we're only have few days left
before the merge window.

> Ah, I think I see the problem - once arch/arm's __dma_alloc() has decided to
> use CMA (because dev_get_cma_area(dev) returns the global area), it then
> won't fall back to trying a regular page allocation if
> dma_alloc_from_contiguous() returns NULL. Thus anything on 32-bit Arm trying
> to allocate a single-page buffer in blockable context with a CMA-enabled
> config is just going to fail. Similarly, it looks like none of the
> DMA_ATTR_FORCE_CONTIGUOUS cases are prepared to handle this change either
> (amd_iommu appears technically affected, but is already using
> dma_alloc_from_contiguous() backwards compared to everyone else, hmm).
> 
> I guess the question is whether to add alloc_page()/free_page() fallbacks to
> those call sites, or stuff them directly into the CMA helpers here.

Well if you come up with some test patch, I can easily test it :)

> > Would you please test and verify? Thanks!

Yes this revert works for me:

Tested-by: Tony Lindgren <tony@atomide.com>

Re: [PATCH] Revert "dma-contiguous: do not allocate a single page from CMA area"

[Nicolin Chen]

On Tue, Feb 26, 2019 at 11:35:44PM +0000, Robin Murphy wrote:
> On 2019-02-26 8:23 pm, Nicolin Chen wrote:
> > This reverts commit d222e42e88168fd67e6d131984b86477af1fc256.
> > 
> > The original change breaks omap dss:
> >      omapdss_dispc 58001000.dispc:
> >          dispc_errata_i734_wa_init: dma_alloc_writecombine failed
> > 
> > Let's revert it first and then find a safer solution instead.
> 
> Ah, I think I see the problem - once arch/arm's __dma_alloc() has decided to
> use CMA (because dev_get_cma_area(dev) returns the global area), it then
> won't fall back to trying a regular page allocation if
> dma_alloc_from_contiguous() returns NULL. Thus anything on 32-bit Arm trying
> to allocate a single-page buffer in blockable context with a CMA-enabled
> config is just going to fail. Similarly, it looks like none of the
> DMA_ATTR_FORCE_CONTIGUOUS cases are prepared to handle this change either
> (amd_iommu appears technically affected, but is already using
> dma_alloc_from_contiguous() backwards compared to everyone else, hmm).

Yea, I searched the tree and got the same results.

> I guess the question is whether to add alloc_page()/free_page() fallbacks to
> those call sites, or stuff them directly into the CMA helpers here.

Probably would be safer/easier to do the later one I feel.

Re: [PATCH] Revert "dma-contiguous: do not allocate a single page from CMA area"

[Krzysztof Kozlowski]

On Tue, 26 Feb 2019 at 21:25, Nicolin Chen <nicoleotsuka@gmail.com> wrote:
>
> This reverts commit d222e42e88168fd67e6d131984b86477af1fc256.
>
> The original change breaks omap dss:
>     omapdss_dispc 58001000.dispc:
>         dispc_errata_i734_wa_init: dma_alloc_writecombine failed
>
> Let's revert it first and then find a safer solution instead.
>
> Reported-by: Tony Lindgren <tony@atomide.com>
> Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
> ---
> Tony,
>
> Would you please test and verify? Thanks!
>
>  kernel/dma/contiguous.c | 22 +++-------------------
>  1 file changed, 3 insertions(+), 19 deletions(-)

This fixes broken (since yesterday) linux-next on Exynos boards
(ARMv7), errors like:
dma-pl330: probe of 121a0000.pdma failed with error -12
exynos-ehci 12110000.usb: can't setup: -12
exynos-ehci 12110000.usb: USB bus 1 deregistered
exynos-ehci 12110000.usb: Failed to add USB HCD

Tested-by: Krzysztof Kozlowski <krzk@kernel.org>

Best regards,
Krzysztof

Re: [PATCH] Revert "dma-contiguous: do not allocate a single page from CMA area"

[Jon Hunter]

On 26/02/2019 20:23, Nicolin Chen wrote:
> This reverts commit d222e42e88168fd67e6d131984b86477af1fc256.
> 
> The original change breaks omap dss:
>     omapdss_dispc 58001000.dispc:
>         dispc_errata_i734_wa_init: dma_alloc_writecombine failed
> 
> Let's revert it first and then find a safer solution instead.
> 
> Reported-by: Tony Lindgren <tony@atomide.com>
> Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
> ---
> Tony,
> 	
> Would you please test and verify? Thanks!

This also fixes various memory allocation failures we have seen on
32-bit Tegra as well.

Tested-by: Jon Hunter <jonathanh@nvidia.com>

Cheers
Jon

-- 
nvpublic