linux-kernel - Re: [RFC PATCH 0/3] spi/xilinx: Merge OF and non-OF drivers

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Message-ID: <4CD7FB27.9030804@monstr.eu>
Date:	Mon, 08 Nov 2010 14:29:11 +0100
From:	Michal Simek <monstr@...str.eu>
To:	Grant Likely <grant.likely@...retlab.ca>
CC:	spi-devel-general@...ts.sourceforge.net,
	richard.rojfors@...ean-labs.com, john.linn@...inx.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] spi/xilinx: Merge OF and non-OF drivers

Hi Grant,

Grant Likely wrote:
> Since of_platform_bus_type has been merged with the platform_bus_type,
> a single platform driver can now support both use cases.  This patch
> series merges the two halves of the xilinx_spi device driver.
> 
> Compile tested only.  I haven't booted this yet.

I have tested it on sp605 and works well. Have you added that patches
to your repository? Or are they somewhere else? Who is responsible for?

I would like to also discuss one change which is related mmc_spi kernel driver.
Let me describe the problem. Microblaze can use dma in all addresses
that's why dma_mask is setup to 0xffffffff in of_platform_device_create.
Xilinx spi driver doesn't support dma but mmc_spi driver is checking dma_mask in parent device
which is xilinx spi driver.

Here is the corresponding the part of code (Expect dma_mask=zero for no dma operations).
mmc_spi.c:~1395
	if (spi->master->dev.parent->dma_mask) {
		struct device	*dev = spi->master->dev.parent;

		host->dma_dev = dev;

Based on this one our customer came with the following solution to setup
dma_mask in xilinx_spi to zero and then mmc_spi doesn't setup dma operation.

I think that this is nice solution but I would like to be sure that I didn't miss anything.
After that i will create proper patch with description.

diff --git a/drivers/spi/xilinx_spi.c b/drivers/spi/xilinx_spi.c
index 7adaef6..3612e1b 100644
--- a/drivers/spi/xilinx_spi.c
+++ b/drivers/spi/xilinx_spi.c
@@ -519,6 +519,9 @@ static int __devinit xilinx_spi_probe(struct platform_device *dev)
        }

        platform_set_drvdata(dev, master);
+       /* clear the dma_mask, to try to disable use of dma */
+       dev->dev.dma_mask = 0;
+
        return 0;
 }

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian
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