Re: [PATCH 05/33] drm/omap: partial workaround for DRA7 DMM errata i878

Hi Tomi,

Thank you for the patch.

On Friday 19 February 2016 11:47:40 Tomi Valkeinen wrote:

Errata i878 says that MPU should not be used to access RAM and DMM at the same time. As it's not possible to prevent MPU accessing RAM, we need to access DMM via a proxy.

This patch changes DMM driver to access DMM registers via sDMA. Instead of doing a normal readl/writel call to read/write a register, we use sDMA to copy 4 bytes from/to the DMM registers.

This patch provides only a partial workaround for i878, as not only DMM register reads/writes are affected, but also accesses to the DMM mapped buffers (framebuffers, usually).

Will this patch really improve the situation if the DMM mapping is accessed anyway ?

Signed-off-by: Tomi Valkeinen tomi.valkeinen@ti.com

Documentation/devicetree/bindings/arm/omap/dmm.txt | 3 +- drivers/gpu/drm/omapdrm/omap_dmm_priv.h | 8 ++ drivers/gpu/drm/omapdrm/omap_dmm_tiler.c | 141 +++++++++++++++++- 3 files changed, 149 insertions(+), 3 deletions(-)

diff --git a/Documentation/devicetree/bindings/arm/omap/dmm.txt b/Documentation/devicetree/bindings/arm/omap/dmm.txt index 8bd6d0a238a8..e5fc2eb7f4da 100644 --- a/Documentation/devicetree/bindings/arm/omap/dmm.txt +++ b/Documentation/devicetree/bindings/arm/omap/dmm.txt @@ -8,7 +8,8 @@ translation for initiators which need contiguous dma bus addresses.

Required properties:

• compatible: Should contain "ti,omap4-dmm" for OMAP4 family

• Should contain "ti,omap5-dmm" for OMAP5 and DRA7x family
  

• Should contain "ti,omap5-dmm" for OMAP5 family
  

• Should contain "ti,dra7-dmm" for DRA7x family
  

Isn't it DRA7xx instead of DRA7x ?

• reg: Contains DMM register address range (base address and length)
• interrupts: Should contain an interrupt-specifier for DMM_IRQ.
• ti,hwmods: Name of the hwmod associated to DMM, which is typically

"dmm"

diff --git a/drivers/gpu/drm/omapdrm/omap_dmm_priv.h b/drivers/gpu/drm/omapdrm/omap_dmm_priv.h index 9f32a83ca507..4d292ba5bcca 100644 --- a/drivers/gpu/drm/omapdrm/omap_dmm_priv.h +++ b/drivers/gpu/drm/omapdrm/omap_dmm_priv.h @@ -155,10 +155,12 @@ struct refill_engine {

struct dmm_platform_data { uint32_t cpu_cache_flags;

• bool errata_i878_wa;

};

struct dmm { struct device *dev;

• u32 phys_base; void __iomem *base; int irq;

@@ -189,6 +191,12 @@ struct dmm { struct list_head alloc_head;

const struct dmm_platform_data *plat_data;

• bool dmm_workaround;
• spinlock_t wa_lock;
• u32 *wa_dma_data;
• dma_addr_t wa_dma_handle;
• struct dma_chan *wa_dma_chan;

};

#endif diff --git a/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c b/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c index fe5260477b52..3ec5c6633585 100644 --- a/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c +++ b/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c @@ -19,6 +19,7 @@ #include <linux/completion.h> #include <linux/delay.h> #include <linux/dma-mapping.h> +#include <linux/dmaengine.h> #include <linux/errno.h> #include <linux/init.h> #include <linux/interrupt.h> @@ -79,14 +80,124 @@ static const uint32_t reg[][4] = { DMM_PAT_DESCR__2, DMM_PAT_DESCR__3}, };

+static int dmm_dma_copy(struct dmm *dmm, u32 src, u32 dst)

Anything wrong with using dma_addr_t ?

+{

• struct dma_device *dma_dev = dmm->wa_dma_chan->device;
• struct dma_async_tx_descriptor *tx = NULL;

No need to initialize tx to NULL.

• enum dma_status status;
• dma_cookie_t cookie;
• tx = dma_dev->device_prep_dma_memcpy(dmm->wa_dma_chan, dst, src, 4, 0);

Given that you're transferring between an I/O mapped register and system memory, I believe you should use dmaengine_prep_slave_single() instead, with a call to dmaengine_slave_config() to set the I/O mapped register physical address. You will also need to request a slave DMA channel instead of a memcpy DMA channel.

• if (!tx) {

• dev_err(dmm->dev, "Failed to prepare DMA memcpy\n");
  

• return -EIO;
  

• }
• cookie = tx->tx_submit(tx);
• if (dma_submit_error(cookie)) {

• dev_err(dmm->dev, "Failed to do DMA tx_submit\n");
  

• return -EIO;
  

• }
• dma_async_issue_pending(dmm->wa_dma_chan);
• status = dma_sync_wait(dmm->wa_dma_chan, cookie);
• if (status != DMA_COMPLETE)

• dev_err(dmm->dev, "i878 wa DMA copy failure\n");
  

• dmaengine_terminate_all(dmm->wa_dma_chan);
• return 0;

+}

+static u32 dmm_read_wa(struct dmm *dmm, u32 reg) +{

• u32 src, dst;
• int r;
• src = (u32)(dmm->phys_base + reg);
• dst = (u32)dmm->wa_dma_handle;
• r = dmm_dma_copy(dmm, src, dst);
• if (r) {

• dev_err(dmm->dev, "sDMA read transfer timeout\n");
  

• return readl(dmm->base + reg);
  

• }
• return readl(dmm->wa_dma_data);

readl() has a memory barrier *after* the read, not before. Similarly writel() has its memory barrier *before* the write. I don't think that's what you want, shouldn't you use readl_relaxed() and writel_relaxed() with explicit barriers ?

I'm also unsure whether readl and writel are the right primitives, as they target access to I/O memory, not system memory. Can't you use explicit barriers and direct access (return *dmm->wa_dma_data) ?

+}

+static void dmm_write_wa(struct dmm *dmm, u32 val, u32 reg) +{

• u32 src, dst;
• int r;
• writel(val, dmm->wa_dma_data);

Same comment here.

• src = (u32)dmm->wa_dma_handle;
• dst = (u32)(dmm->phys_base + reg);
• r = dmm_dma_copy(dmm, src, dst);
• if (r) {

• dev_err(dmm->dev, "sDMA write transfer timeout\n");
  

• writel(val, dmm->base + reg);
  

• }

+}

static u32 dmm_read(struct dmm *dmm, u32 reg) {

• return readl(dmm->base + reg);

• if (dmm->dmm_workaround) {

• u32 v;
  

• unsigned long flags;
  

• spin_lock_irqsave(&dmm->wa_lock, flags);
  

• v = dmm_read_wa(dmm, reg);
  

dma_sync_wait() with a spinlock held doesn't seem like the best idea to me.

• spin_unlock_irqrestore(&dmm->wa_lock, flags);
  

• return v;
  

• } else {

• return readl(dmm->base + reg);
  

• }

}

static void dmm_write(struct dmm *dmm, u32 val, u32 reg) {

• writel(val, dmm->base + reg);

• if (dmm->dmm_workaround) {

• unsigned long flags;
  

• spin_lock_irqsave(&dmm->wa_lock, flags);
  

• dmm_write_wa(dmm, val, reg);
  

Ditto.

• spin_unlock_irqrestore(&dmm->wa_lock, flags);
  

• } else {

• writel(val, dmm->base + reg);
  

• }

+}

+static int dmm_workaround_init(struct dmm *dmm) +{

• dma_cap_mask_t mask;
• dma_cap_zero(mask);
• dma_cap_set(DMA_MEMCPY, mask);

Nitpicking, I'd move those two lines down right before the dma_request_channel() call, as they are part of the same logical block of code.

• spin_lock_init(&dmm->wa_lock);
• dmm->wa_dma_data = dma_alloc_coherent(dmm->dev, 4, &dmm->wa_dma_handle,

GFP_KERNEL);

Maybe a macro instead of 4 ?

• if (!dmm->wa_dma_data)

• return -ENOMEM;
  

• dmm->wa_dma_chan = dma_request_channel(mask, NULL, NULL);
• if (!dmm->wa_dma_chan) {

• dma_free_coherent(dmm->dev, 4, dmm->wa_dma_data, dmm->wa_dma_handle);
  

• return -ENODEV;
  

• }
• return 0;

+}

+static void dmm_workaround_uninit(struct dmm *dmm) +{

• dma_release_channel(dmm->wa_dma_chan);
• dma_free_coherent(dmm->dev, 4, dmm->wa_dma_data, dmm->wa_dma_handle);

}

/* simple allocator to grab next 16 byte aligned memory from txn */ @@ -606,6 +717,9 @@ static int omap_dmm_remove(struct platform_device *dev) if (omap_dmm->dummy_page) __free_page(omap_dmm->dummy_page);

• if (omap_dmm->dmm_workaround)
  

• 	dmm_workaround_uninit(omap_dmm);
  

• if (omap_dmm->irq > 0) free_irq(omap_dmm->irq, omap_dmm);

@@ -653,6 +767,7 @@ static int omap_dmm_probe(struct platform_device *dev) goto fail; }

• omap_dmm->phys_base = mem->start; omap_dmm->base = ioremap(mem->start, SZ_2K);

  if (!omap_dmm->base) {

@@ -668,6 +783,19 @@ static int omap_dmm_probe(struct platform_device *dev)

omap_dmm->dev = &dev->dev;

• omap_dmm->dmm_workaround = omap_dmm->plat_data->errata_i878_wa;
• if (omap_dmm->dmm_workaround) {

I'd test omap_dmm->plat_data->errata_i878_wa here, omap_dmm->dmm_workaround is initialized to false by kzalloc().

• int r;
  

• r = dmm_workaround_init(omap_dmm);
  

Can't you use the ret variable ? I know it's pre-initialized to -EFAULT, but it seems better to me to set it to explicit values in the three goto fail; error cases that would be impacted, especially given that -EFAULT is the wrong error code to return (and as it would touch that code, the platform_get_resource() + ioremap() calls can be optimized in a devm_ioremap_resource() in another cleanup patch).

• if (r) {
  

• 	omap_dmm->dmm_workaround = false;
  

• 	dev_err(&dev->dev, "failed to initialize work-around, WA not 
  

used\n");

As this is a non-fatal error, maybe dev_warn() ?

• } else {
  

• 	dev_info(&dev->dev, "workaround for errata i878 in use\n");
  

• }
  

• }
• hwinfo = dmm_read(omap_dmm, DMM_PAT_HWINFO); omap_dmm->num_engines = (hwinfo >> 24) & 0x1F; omap_dmm->num_lut = (hwinfo >> 16) & 0x1F;

@@ -1031,6 +1159,11 @@ static const struct dmm_platform_data dmm_omap5_platform_data = { .cpu_cache_flags = OMAP_BO_UNCACHED, };

+static const struct dmm_platform_data dmm_dra7_platform_data = {

• .cpu_cache_flags = OMAP_BO_UNCACHED,
• .errata_i878_wa = true,

+};

static const struct of_device_id dmm_of_match[] = { { .compatible = "ti,omap4-dmm", @@ -1040,6 +1173,10 @@ static const struct of_device_id dmm_of_match[] = { .compatible = "ti,omap5-dmm", .data = &dmm_omap5_platform_data, },

• {

• .compatible = "ti,dra7-dmm",
  

• .data = &dmm_dra7_platform_data,
  

• }, {},

}; #endif