On 09/26/2017 08:08 AM, Jon Hunter wrote:
Hi Dmitry,
On 25/09/17 23:35, Dmitry Osipenko wrote:
DMA config is incorrect, because of it DMA transfer is never issued and
tegra20_fuse_read() always returns 0x0.
Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
---
drivers/soc/tegra/fuse/fuse-tegra.c | 1 +
drivers/soc/tegra/fuse/fuse-tegra20.c | 3 ++-
2 files changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/soc/tegra/fuse/fuse-tegra.c b/drivers/soc/tegra/fuse/fuse-tegra.c
index b7c552e3133c..73a3a2c74021 100644
--- a/drivers/soc/tegra/fuse/fuse-tegra.c
+++ b/drivers/soc/tegra/fuse/fuse-tegra.c
@@ -132,6 +132,7 @@ static int tegra_fuse_probe(struct platform_device *pdev)
/* take over the memory region from the early initialization */
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+ fuse->phys = res->start;
fuse->base = devm_ioremap_resource(&pdev->dev, res);
if (IS_ERR(fuse->base))
return PTR_ERR(fuse->base);
diff --git a/drivers/soc/tegra/fuse/fuse-tegra20.c b/drivers/soc/tegra/fuse/fuse-tegra20.c
index 294413a969a0..a33f48c06771 100644
--- a/drivers/soc/tegra/fuse/fuse-tegra20.c
+++ b/drivers/soc/tegra/fuse/fuse-tegra20.c
@@ -59,7 +59,7 @@ static u32 tegra20_fuse_read(struct tegra_fuse *fuse, unsigned int offset)
mutex_lock(&fuse->apbdma.lock);
- fuse->apbdma.config.src_addr = fuse->apbdma.phys + FUSE_BEGIN + offset;
+ fuse->apbdma.config.src_addr = fuse->phys + FUSE_BEGIN + offset;
err = dmaengine_slave_config(fuse->apbdma.chan, &fuse->apbdma.config);
if (err)
@@ -119,6 +119,7 @@ static int tegra20_fuse_probe(struct tegra_fuse *fuse)
fuse->apbdma.config.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
fuse->apbdma.config.src_maxburst = 1;
fuse->apbdma.config.dst_maxburst = 1;
+ fuse->apbdma.config.direction = DMA_DEV_TO_MEM;
init_completion(&fuse->apbdma.wait);
mutex_init(&fuse->apbdma.lock);
Thanks for the fix.
When booting the mainline on Tegra20 Trimslice, I only see the
tegra20_fuse_read_early() called and not the tegra20_fuse_read(). That's
not to say it is not needed, but I am wondering if we really need this
complex tegra20_fuse_read() using DMA and whether we should just have
the normal fuse->read() call tegra20_fuse_read_early() as well to
simplify matters?
Maybe Thierry or Stephen know the history here?
There's some HW bug related to reading the fuse registers from the CPU.
The fix was implemented long ago by Olof; see the git commit description
pasted below. IIRC, the code directly reads the fuse registers before
the point where DMA is available (the argument being we can't do
anything else, and this period of time is short so the risk hopefully
low), but once DMA is available, it is used to avoid the HW bug. The bug
was apparently fixed in Tegra30; see the other commit description pasted
below.
commit e2f91578b35347341482f6af9e4fcf3174531efd
Author: Olof Johansson <olof@xxxxxxxxx>
Date: Wed Oct 12 23:52:29 2011 -0700
ARM: tegra: use APB DMA for accessing APB devices
Tegra2 hangs if APB registers are accessed from the cpu during an
apb dma operation. The workaround is to use apb dma to read/write the
registers instead.
There is a dependency loop between fuses, clocks, and APBDMA. If dma
is enabled, fuse reads must go through APBDMA to avoid corruption due
to a hw bug. APBDMA requires a clock to be enabled. Clocks must read
a fuse to determine allowable cpu frequencies.
Separate out the fuse DMA initialization, and allow the fuse read
and write functions to be called without using DMA before the DMA
initialization has been completed. Access to the fuses before APBDMA
is initialized won't hit the hardware bug because nothing else can be
using DMA.
Original fuse registar access code from Varun Wadekar
<vwadekar@xxxxxxxxxx>, improved by Colin Cross <ccross@xxxxxxxxxxx>
and later moved to separate driver by Jon Mayo <jmayo@xxxxxxxxxx>.
Major refactoring/cleanup by Olof Johansson <olof@xxxxxxxxx>.
Changes since v1:
* fix 'return false' on error condition
* dequeue dma ops in case of timeout
From: Jon Mayo <jmayo@xxxxxxxxxx>.
Signed-off-by: Jon Mayo <jmayo@xxxxxxxxxx>.
Signed-off-by: Olof Johansson <olof@xxxxxxxxx>
Acked-by: Stephen Warren <swarren@xxxxxxxxxx>
commit b861c275ea5cfeab32241c3c92a203579d5699ff
Author: Laxman Dewangan <ldewangan@xxxxxxxxxx>
Date: Wed Jun 20 18:06:34 2012 +0530
ARM: tegra: apbio access using dma for tegra20 only
The Tegra20 HW issue with accessing APBIO registers (such
as fuse registers) directly from the CPU concurrently with
APB DMA accesses has been fixed in Tegra30 and later chips.
Access these registers directly from the CPU on Tegra30
and later, and apply the workaround only for Tegra20.
Signed-off-by: Laxman Dewangan <ldewangan@xxxxxxxxxx>
Tested-by: Chaitanya Bandi <bandik@xxxxxxxxxx>
Signed-off-by: Stephen Warren <swarren@xxxxxxxxxx>
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