fel_lib: Implement thunk code for register-based retrieval of SID

The new function fel_get_sid_registers() uses ARM code for register
access to the SID root key. This is necessary to retrieve correct
values for certain SoCs, e.g. when not using this approach the H3
has been observed to return 'mangled' values (when reading SID from
memory).

See https://groups.google.com/forum/#!topic/linux-sunxi/ynyIP8c61Qs



The FEL library provides a uniform fel_get_sid_root_key() wrapper
that will automatically use the workaround method for SoCs that
are tagged accordingly - so the application program does not have
to bother with selecting memory vs. register-based access.
Signed-off-by: Bernhard Nortmann <bernhard.nortmann@web.de>

fel_lib.c

@@ -368,6 +368,73 @@ void fel_writel_n(feldev_handle *dev, uint32_t addr, uint32_t *src, size_t count
 	}
 }
 
+/*
+ * Memory access to the SID (root) keys proved to be unreliable for certain
+ * SoCs. This function uses an alternative, register-based approach to retrieve
+ * the values.
+ */
+static void fel_get_sid_registers(feldev_handle *dev, uint32_t *result)
+{
+	uint32_t arm_code[] = {
+		htole32(0xe59f0040), /*    0:  ldr   r0, [pc, #64]           */
+		htole32(0xe3a01000), /*    4:  mov   r1, #0                  */
+		htole32(0xe28f303c), /*    8:  add   r3, pc, #60             */
+		/* <sid_read_loop>: */
+		htole32(0xe1a02801), /*    c:  lsl   r2, r1, #16             */
+		htole32(0xe3822b2b), /*   10:  orr   r2, r2, #44032          */
+		htole32(0xe3822002), /*   14:  orr   r2, r2, #2              */
+		htole32(0xe5802040), /*   18:  str   r2, [r0, #64]           */
+		/* <sid_read_wait>: */
+		htole32(0xe5902040), /*   1c:  ldr   r2, [r0, #64]           */
+		htole32(0xe3120002), /*   20:  tst   r2, #2                  */
+		htole32(0x1afffffc), /*   24:  bne   1c <sid_read_wait>      */
+		htole32(0xe5902060), /*   28:  ldr   r2, [r0, #96]           */
+		htole32(0xe7832001), /*   2c:  str   r2, [r3, r1]            */
+		htole32(0xe2811004), /*   30:  add   r1, r1, #4              */
+		htole32(0xe3510010), /*   34:  cmp   r1, #16                 */
+		htole32(0x3afffff3), /*   38:  bcc   c <sid_read_loop>       */
+		htole32(0xe3a02000), /*   3c:  mov   r2, #0                  */
+		htole32(0xe5802040), /*   40:  str   r2, [r0, #64]           */
+		htole32(0xe12fff1e), /*   44:  bx    lr                      */
+		htole32(dev->soc_info->sid_base), /* SID base addr */
+		/* retrieved SID values go here */
+	};
+	/* write and execute code */
+	aw_fel_write(dev, arm_code, dev->soc_info->scratch_addr, sizeof(arm_code));
+	aw_fel_execute(dev, dev->soc_info->scratch_addr);
+	/* read back the result */
+	aw_fel_read(dev, dev->soc_info->scratch_addr + sizeof(arm_code),
+		    result, 4 * sizeof(uint32_t));
+	for (unsigned i = 0; i < 4; i++)
+		result[i] = le32toh(result[i]);
+}
+
+/* Read the SID "root" key (128 bits). You need to pass the device handle,
+ * a pointer to a result array capable of receiving at least four 32-bit words,
+ * and a flag specifying if the register-access workaround should be enforced.
+ * Return value indicates whether the result is expected to be usable:
+ * The function will return `false` (and zero the result) if it cannot access
+ * the SID registers.
+ */
+bool fel_get_sid_root_key(feldev_handle *dev, uint32_t *result,
+			  bool force_workaround)
+{
+	if (!dev->soc_info->sid_base) {
+		/* SID unavailable */
+		for (unsigned i = 0; i < 4; i++) result[i] = 0;
+		return false;
+	}
+
+	if (dev->soc_info->sid_fix || force_workaround)
+		/* Work around SID issues by using ARM thunk code */
+		fel_get_sid_registers(dev, result);
+	else
+		/* Read SID directly from memory */
+		fel_readl_n(dev, dev->soc_info->sid_base
+			       + dev->soc_info->sid_offset, result, 4);
+	return true;
+}
+
 /* general functions, "FEL device" management */
 
 static int feldev_get_endpoint(feldev_handle *dev)
@@ -601,10 +668,7 @@ feldev_list_entry *list_fel_devices(size_t *count)
 		strncpy(entry->soc_name, dev->soc_name, sizeof(soc_name_t));
 
 		/* retrieve SID bits */
-		if (dev->soc_info->sid_base)
-			aw_fel_readl_n(dev,
-				dev->soc_info->sid_base + dev->soc_info->sid_offset,
-				entry->SID, 4);
+		fel_get_root_key(dev, entry->SID, false);
 
 		feldev_close(dev);
 		free(dev);

fel_lib.h

@@ -67,4 +67,8 @@ void aw_fel_execute(feldev_handle *dev, uint32_t offset);
 void fel_readl_n(feldev_handle *dev, uint32_t addr, uint32_t *dst, size_t count);
 void fel_writel_n(feldev_handle *dev, uint32_t addr, uint32_t *src, size_t count);
 
+/* retrieve SID root key */
+bool fel_get_sid_root_key(feldev_handle *dev, uint32_t *result,
+			  bool force_workaround);
+
 #endif /* _SUNXI_TOOLS_FEL_LIB_H */

sid_read_root.S

+/*
+ * Copyright (C) 2016 Bernhard Nortmann <bernhard.nortmann@web.de>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+/*
+ * ARM thunk code to read the SID root key using register-based access.
+ *
+ * This is necessary for certain SoCs (e.g. H3), as the values read via
+ * memory mapping might not be consistent. For background information see
+ * https://groups.google.com/forum/#!topic/linux-sunxi/ynyIP8c61Qs
+ */
+
+SID_BASE	.req	r0
+sid_key_index	.req	r1
+
+.set	SID_PRCTL,	0x40	/* SID program/read control register */
+.set	SID_PRKEY,	0x50	/* SID program key value register */
+.set	SID_RDKEY,	0x60	/* SID read key value register */
+
+.set	SID_OP_LOCK,	0xAC	/* Efuse operation lock value */
+.set	SID_READ_START,	(1 << 1) /* bit 1 of SID_PRCTL, Software Read Start */
+.set	SID_PG_START,	(1 << 0) /* bit 0 of SID_PRCTL, Software Program Start */
+
+sid_read_root_key:
+	ldr	SID_BASE, sid_base
+	mov	sid_key_index, #0
+	adr	r3, sid_result			/* result pointer */
+sid_read_loop:
+	mov	r2, sid_key_index, lsl #16	/* PG_INDEX value */
+	orr	r2, #SID_OP_LOCK << 8	/* OP_LOCK to enable SID_READ_START */
+	orr	r2, #SID_READ_START
+	str	r2, [SID_BASE, #SID_PRCTL]	/* write SID_PRCTL */
+sid_read_wait:
+	ldr	r2, [SID_BASE, #SID_PRCTL]	/* read SID_PRCTL */
+	tst	r2, #SID_READ_START	/* check if read operation completed */
+	bne	sid_read_wait		/* loop while bit 1 still set */
+
+	ldr	r2, [SID_BASE, #SID_RDKEY]	/* read SID key value */
+	str	r2, [r3, sid_key_index]		/* store SID value */
+
+	add	sid_key_index, #4
+	cmp	sid_key_index, #16
+	blo	sid_read_loop		/* loop while (sid_key_index < 0x10) */
+
+	mov	r2, #0
+	str	r2, [SID_BASE, #SID_PRCTL]	/* clear SID_PRCTL */
+	bx	lr
+
+sid_base:	.word 0
+sid_result:	.word 0 /* receives the four "root key" 32-bit words */
+		.word 0
+		.word 0
+		.word 0

sid_read_root.h

+		/* <sid_read_root_key>: */
+		htole32(0xe59f0040), /*    0:  ldr   r0, [pc, #64]           */
+		htole32(0xe3a01000), /*    4:  mov   r1, #0                  */
+		htole32(0xe28f303c), /*    8:  add   r3, pc, #60             */
+		/* <sid_read_loop>: */
+		htole32(0xe1a02801), /*    c:  lsl   r2, r1, #16             */
+		htole32(0xe3822b2b), /*   10:  orr   r2, r2, #44032          */
+		htole32(0xe3822002), /*   14:  orr   r2, r2, #2              */
+		htole32(0xe5802040), /*   18:  str   r2, [r0, #64]           */
+		/* <sid_read_wait>: */
+		htole32(0xe5902040), /*   1c:  ldr   r2, [r0, #64]           */
+		htole32(0xe3120002), /*   20:  tst   r2, #2                  */
+		htole32(0x1afffffc), /*   24:  bne   1c <sid_read_wait>      */
+		htole32(0xe5902060), /*   28:  ldr   r2, [r0, #96]           */
+		htole32(0xe7832001), /*   2c:  str   r2, [r3, r1]            */
+		htole32(0xe2811004), /*   30:  add   r1, r1, #4              */
+		htole32(0xe3510010), /*   34:  cmp   r1, #16                 */
+		htole32(0x3afffff3), /*   38:  bcc   c <sid_read_loop>       */
+		htole32(0xe3a02000), /*   3c:  mov   r2, #0                  */
+		htole32(0xe5802040), /*   40:  str   r2, [r0, #64]           */
+		htole32(0xe12fff1e), /*   44:  bx    lr                      */
+		/* <sid_base>: */
+		htole32(0x00000000), /*   48:  .word 0x00000000              */
+		/* <sid_result>: */