1 /* Tests for presence or absence of hardware registers. 2 * This code was originally in atari/config.c, but I noticed 3 * that it was also in drivers/nubus/nubus.c and I wanted to 4 * use it in hp300/config.c, so it seemed sensible to pull it 5 * out into its own file. 6 * 7 * The test is for use when trying to read a hardware register 8 * that isn't present would cause a bus error. We set up a 9 * temporary handler so that this doesn't kill the kernel. 10 * 11 * There is a test-by-reading and a test-by-writing; I present 12 * them here complete with the comments from the original atari 13 * config.c... 14 * -- PMM <pmaydell@chiark.greenend.org.uk>, 05/1998 15 */ 16 17 /* This function tests for the presence of an address, specially a 18 * hardware register address. It is called very early in the kernel 19 * initialization process, when the VBR register isn't set up yet. On 20 * an Atari, it still points to address 0, which is unmapped. So a bus 21 * error would cause another bus error while fetching the exception 22 * vector, and the CPU would do nothing at all. So we needed to set up 23 * a temporary VBR and a vector table for the duration of the test. 24 */ 25 26 #include <linux/module.h> 27 28 int hwreg_present(volatile void *regp) 29 { 30 int ret = 0; 31 unsigned long flags; 32 long save_sp, save_vbr; 33 long tmp_vectors[3]; 34 35 local_irq_save(flags); 36 __asm__ __volatile__ ( 37 "movec %/vbr,%2\n\t" 38 "movel #Lberr1,%4@(8)\n\t" 39 "movec %4,%/vbr\n\t" 40 "movel %/sp,%1\n\t" 41 "moveq #0,%0\n\t" 42 "tstb %3@\n\t" 43 "nop\n\t" 44 "moveq #1,%0\n" 45 "Lberr1:\n\t" 46 "movel %1,%/sp\n\t" 47 "movec %2,%/vbr" 48 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr) 49 : "a" (regp), "a" (tmp_vectors) 50 ); 51 local_irq_restore(flags); 52 53 return ret; 54 } 55 EXPORT_SYMBOL(hwreg_present); 56 57 /* Basically the same, but writes a value into a word register, protected 58 * by a bus error handler. Returns 1 if successful, 0 otherwise. 59 */ 60 61 int hwreg_write(volatile void *regp, unsigned short val) 62 { 63 int ret; 64 unsigned long flags; 65 long save_sp, save_vbr; 66 long tmp_vectors[3]; 67 68 local_irq_save(flags); 69 __asm__ __volatile__ ( 70 "movec %/vbr,%2\n\t" 71 "movel #Lberr2,%4@(8)\n\t" 72 "movec %4,%/vbr\n\t" 73 "movel %/sp,%1\n\t" 74 "moveq #0,%0\n\t" 75 "movew %5,%3@\n\t" 76 "nop\n\t" 77 /* 78 * If this nop isn't present, 'ret' may already be loaded 79 * with 1 at the time the bus error happens! 80 */ 81 "moveq #1,%0\n" 82 "Lberr2:\n\t" 83 "movel %1,%/sp\n\t" 84 "movec %2,%/vbr" 85 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr) 86 : "a" (regp), "a" (tmp_vectors), "g" (val) 87 ); 88 local_irq_restore(flags); 89 90 return ret; 91 } 92 EXPORT_SYMBOL(hwreg_write); 93 94