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drm/sun4i: Remove VLA usage
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In the quest to remove all stack VLA usage from the kernel[1], this
switches to using a kmalloc allocation and moves all the size calculations
to the start to do an allocation. If an upper bounds on the mode timing
calculations could be determined, a fixed stack size could be used instead.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180629184740.GA37415@beast
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Kees Cook authored and Maxime Ripard committed Jul 4, 2018
1 parent 968d72e commit c51756d
Showing 1 changed file with 64 additions and 43 deletions.
107 changes: 64 additions & 43 deletions drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
#include <linux/pm_runtime.h>
#include <linux/regmap.h>
#include <linux/reset.h>
#include <linux/slab.h>

#include <linux/phy/phy.h>

Expand Down Expand Up @@ -247,10 +248,8 @@ static u16 sun6i_dsi_crc_compute(u8 const *buffer, size_t len)
return crc_ccitt(0xffff, buffer, len);
}

static u16 sun6i_dsi_crc_repeat_compute(u8 pd, size_t len)
static u16 sun6i_dsi_crc_repeat(u8 pd, u8 *buffer, size_t len)
{
u8 buffer[len];

memset(buffer, pd, len);

return sun6i_dsi_crc_compute(buffer, len);
Expand All @@ -274,11 +273,11 @@ static u32 sun6i_dsi_build_blk0_pkt(u8 vc, u16 wc)
wc & 0xff, wc >> 8);
}

static u32 sun6i_dsi_build_blk1_pkt(u16 pd, size_t len)
static u32 sun6i_dsi_build_blk1_pkt(u16 pd, u8 *buffer, size_t len)
{
u32 val = SUN6I_DSI_BLK_PD(pd);

return val | SUN6I_DSI_BLK_PF(sun6i_dsi_crc_repeat_compute(pd, len));
return val | SUN6I_DSI_BLK_PF(sun6i_dsi_crc_repeat(pd, buffer, len));
}

static void sun6i_dsi_inst_abort(struct sun6i_dsi *dsi)
Expand Down Expand Up @@ -452,6 +451,54 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
struct mipi_dsi_device *device = dsi->device;
unsigned int Bpp = mipi_dsi_pixel_format_to_bpp(device->format) / 8;
u16 hbp, hfp, hsa, hblk, vblk;
size_t bytes;
u8 *buffer;

/* Do all timing calculations up front to allocate buffer space */

/*
* A sync period is composed of a blanking packet (4 bytes +
* payload + 2 bytes) and a sync event packet (4 bytes). Its
* minimal size is therefore 10 bytes
*/
#define HSA_PACKET_OVERHEAD 10
hsa = max((unsigned int)HSA_PACKET_OVERHEAD,
(mode->hsync_end - mode->hsync_start) * Bpp - HSA_PACKET_OVERHEAD);

/*
* The backporch is set using a blanking packet (4 bytes +
* payload + 2 bytes). Its minimal size is therefore 6 bytes
*/
#define HBP_PACKET_OVERHEAD 6
hbp = max((unsigned int)HBP_PACKET_OVERHEAD,
(mode->hsync_start - mode->hdisplay) * Bpp - HBP_PACKET_OVERHEAD);

/*
* The frontporch is set using a blanking packet (4 bytes +
* payload + 2 bytes). Its minimal size is therefore 6 bytes
*/
#define HFP_PACKET_OVERHEAD 6
hfp = max((unsigned int)HFP_PACKET_OVERHEAD,
(mode->htotal - mode->hsync_end) * Bpp - HFP_PACKET_OVERHEAD);

/*
* hblk seems to be the line + porches length.
*/
hblk = mode->htotal * Bpp - hsa;

/*
* And I'm not entirely sure what vblk is about. The driver in
* Allwinner BSP is using a rather convoluted calculation
* there only for 4 lanes. However, using 0 (the !4 lanes
* case) even with a 4 lanes screen seems to work...
*/
vblk = 0;

/* How many bytes do we need to send all payloads? */
bytes = max_t(size_t, max(max(hfp, hblk), max(hsa, hbp)), vblk);
buffer = kmalloc(bytes, GFP_KERNEL);
if (WARN_ON(!buffer))
return;

regmap_write(dsi->regs, SUN6I_DSI_BASIC_CTL_REG, 0);

Expand Down Expand Up @@ -485,63 +532,37 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
SUN6I_DSI_BASIC_SIZE1_VACT(mode->vdisplay) |
SUN6I_DSI_BASIC_SIZE1_VT(mode->vtotal));

/*
* A sync period is composed of a blanking packet (4 bytes +
* payload + 2 bytes) and a sync event packet (4 bytes). Its
* minimal size is therefore 10 bytes
*/
#define HSA_PACKET_OVERHEAD 10
hsa = max((unsigned int)HSA_PACKET_OVERHEAD,
(mode->hsync_end - mode->hsync_start) * Bpp - HSA_PACKET_OVERHEAD);
/* sync */
regmap_write(dsi->regs, SUN6I_DSI_BLK_HSA0_REG,
sun6i_dsi_build_blk0_pkt(device->channel, hsa));
regmap_write(dsi->regs, SUN6I_DSI_BLK_HSA1_REG,
sun6i_dsi_build_blk1_pkt(0, hsa));
sun6i_dsi_build_blk1_pkt(0, buffer, hsa));

/*
* The backporch is set using a blanking packet (4 bytes +
* payload + 2 bytes). Its minimal size is therefore 6 bytes
*/
#define HBP_PACKET_OVERHEAD 6
hbp = max((unsigned int)HBP_PACKET_OVERHEAD,
(mode->hsync_start - mode->hdisplay) * Bpp - HBP_PACKET_OVERHEAD);
/* backporch */
regmap_write(dsi->regs, SUN6I_DSI_BLK_HBP0_REG,
sun6i_dsi_build_blk0_pkt(device->channel, hbp));
regmap_write(dsi->regs, SUN6I_DSI_BLK_HBP1_REG,
sun6i_dsi_build_blk1_pkt(0, hbp));
sun6i_dsi_build_blk1_pkt(0, buffer, hbp));

/*
* The frontporch is set using a blanking packet (4 bytes +
* payload + 2 bytes). Its minimal size is therefore 6 bytes
*/
#define HFP_PACKET_OVERHEAD 6
hfp = max((unsigned int)HFP_PACKET_OVERHEAD,
(mode->htotal - mode->hsync_end) * Bpp - HFP_PACKET_OVERHEAD);
/* frontporch */
regmap_write(dsi->regs, SUN6I_DSI_BLK_HFP0_REG,
sun6i_dsi_build_blk0_pkt(device->channel, hfp));
regmap_write(dsi->regs, SUN6I_DSI_BLK_HFP1_REG,
sun6i_dsi_build_blk1_pkt(0, hfp));
sun6i_dsi_build_blk1_pkt(0, buffer, hfp));

/*
* hblk seems to be the line + porches length.
*/
hblk = mode->htotal * Bpp - hsa;
/* hblk */
regmap_write(dsi->regs, SUN6I_DSI_BLK_HBLK0_REG,
sun6i_dsi_build_blk0_pkt(device->channel, hblk));
regmap_write(dsi->regs, SUN6I_DSI_BLK_HBLK1_REG,
sun6i_dsi_build_blk1_pkt(0, hblk));
sun6i_dsi_build_blk1_pkt(0, buffer, hblk));

/*
* And I'm not entirely sure what vblk is about. The driver in
* Allwinner BSP is using a rather convoluted calculation
* there only for 4 lanes. However, using 0 (the !4 lanes
* case) even with a 4 lanes screen seems to work...
*/
vblk = 0;
/* vblk */
regmap_write(dsi->regs, SUN6I_DSI_BLK_VBLK0_REG,
sun6i_dsi_build_blk0_pkt(device->channel, vblk));
regmap_write(dsi->regs, SUN6I_DSI_BLK_VBLK1_REG,
sun6i_dsi_build_blk1_pkt(0, vblk));
sun6i_dsi_build_blk1_pkt(0, buffer, vblk));

kfree(buffer);
}

static int sun6i_dsi_start(struct sun6i_dsi *dsi,
Expand Down

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