[PATCH 08/19] mmc: sdhi: Enable the driver on all ARM platforms

Hi Sergei,

On Tuesday 29 October 2013 23:47:36 Sergei Shtylyov wrote:

On 10/29/2013 04:15 PM, Laurent Pinchart wrote:

quoted

quoted

quoted

quoted

quoted

Renesas ARM platforms are transitioning from single-platform to
multi-platform kernels using the new ARCH_SHMOBILE_MULTI. Make the
driver available on all ARM platforms to enable it on both
ARCH_SHMOBILE and ARCH_SHMOBILE_MULTI and increase build testing
coverage.

Cc: Chris Ball <redacted>
Cc: Guennadi Liakhovetski <redacted>
Cc: Ian Molton <redacted>
Cc: linux-mmc at vger.kernel.org
Signed-off-by: Laurent Pinchart
[off-list ref]

[...]

quoted

quoted

quoted

diff --git a/drivers/mmc/host/tmio_mmc_dma.c

b/drivers/mmc/host/tmio_mmc_dma.c index 65edb4a..535bc35 100644

--- a/drivers/mmc/host/tmio_mmc_dma.c
+++ b/drivers/mmc/host/tmio_mmc_dma.c

@@ -28,7 +28,7 @@ void tmio_mmc_enable_dma(struct tmio_mmc_host *host,

bool enable)>

   	if (!host->chan_tx || !host->chan_rx)
   	
   		return;

-#if defined(CONFIG_SUPERH) || defined(CONFIG_ARCH_SHMOBILE)
+#if defined(CONFIG_SUPERH) || defined(CONFIG_ARM)

I'm not sure about this one. In principle DMA so far is only used on
SDHI with TMIO. But this #if was for a theoretical case, when a TMIO
MMC IP inside an MFD is also used with DMA. Bus since I had no
indormation about whether the CTL_DMA_ENABLE register was SDHI specific
or not, I put it under an #if for the time being. In any case, I don't
think making it #ifdef CONFIG_ARM makes much sense. We can either
remove the #if completely, or keep it to limit the scope of this write
to sh-mobile arches.

SUPERH || ARCH_SHMOBILE covers all the platforms this driver currently
builds on. Now that we're adding ARCH_SHMOBILE_MULTI the #if needs to
cover that case as well. I'm fine with limiting the CTL_DMA_ENABLE write
to SUPERH only (which would modify the driver's behaviour)

I'm afraid that would break the driver's ability to work in DMA mode on
SH-Mobile SoCs.

So can you confirm that writing the CTL_DMA_ENABLE register is required on
all Renesas ARM SoCs (including SH-Mobile, R-Mobile and R-Car) ?

I can't actually say anything about all SH-Mobile and R-Mobile SoCs, only
about the R-Car SoCs: though the datasheets don't contain the SDHI register
info, from my experience the register exists on R8A777x (I had to fix up the
broken PIO fallback in the SDHI driver).

OK.

quoted

quoted

quoted

or enabling it unconditionally, but I don't think adding a
defined(CONFIG_ARCH_SHMOBILE_MULTI) to the above #if makes sense, unless
there's a plan to add support for DMA for non-SH (including both SUPERH
and ARCH_SHMOBILE) platforms.

Not only the plan -- I have already posted the patches to do it for
R8A777x, and Simon has queued them for 3.13.

Could you please point me to those patches ?

https://git.kernel.org/cgit/linux/kernel/git/horms/renesas.git/commit/?h=nex
t&id=1eb6b5a0e55bfcfb0852b7d0f9442841ff807345
https://git.kernel.org/cgit/linux/kernel/git/horms/renesas.git/commit/?h=ne
xt&id=a43e5bd76a4a3df58167d85e8020a1c9e566ad75
https://git.kernel.org/cgit/linux/kernel/git/horms/renesas.git/commit/?h=ne
xt&id=5d6aa3435275a5308684f90c17424b055ef7f572
https://git.kernel.org/cgit/linux/kernel/git/horms/renesas.git/commit/?h=ne
xt&id=e6a8b11b82fdeaa78dad52552f945b772ee1a5c9

But that's still an ARCH_SHMOBILE platform. Guennadi's point, if I understood 
it correctly, was that whether the CTL_DMA_ENABLE register is part of the 
standard TMIO controller, or is Renesas-specific, is unknown. As we have no 
current or planned TMIO DMA users other than SUPERH and ARCH_SHMOBILE this is 
impossible to test. That is why the code is conditionally compiled.

We could either get rid of the #if completely and always write to the 
register, or add ARCH_SHMOBILE_MULTI to the condition. I now agree that adding 
ARM as a dependency makes no sense. Given that this will break on 
multiplatform kernels anyway, I'm enclined to write to the CTL_DMA_ENABLE 
register unconditionally. I'll update the patch accordingly.

-- 
Regards,

Laurent Pinchart