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      1 /* $NetBSD: amdccp.c,v 1.5 2022/03/19 11:55:03 riastradh Exp $ */
      2 
      3 /*
      4  * Copyright (c) 2018 Jonathan A. Kollasch
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     18  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     19  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
     20  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
     21  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
     22  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
     23  * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
     24  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
     25  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
     26  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 
     29 #include <sys/cdefs.h>
     30 
     31 __KERNEL_RCSID(0, "$NetBSD: amdccp.c,v 1.5 2022/03/19 11:55:03 riastradh Exp $");
     32 
     33 #include <sys/param.h>
     34 #include <sys/systm.h>
     35 #include <sys/device.h>
     36 #include <sys/bus.h>
     37 #include <sys/rndsource.h>
     38 
     39 #include <dev/ic/amdccpvar.h>
     40 
     41 static uint32_t amdccp_rnd_read(struct amdccp_softc *);
     42 static void amdccp_rnd_callback(size_t, void *);
     43 
     44 void
     45 amdccp_common_attach(struct amdccp_softc *sc)
     46 {
     47 
     48 	rndsource_setcb(&sc->sc_rndsource, amdccp_rnd_callback, sc);
     49 	rnd_attach_source(&sc->sc_rndsource, device_xname(sc->sc_dev),
     50 	    RND_TYPE_RNG, RND_FLAG_COLLECT_VALUE|RND_FLAG_HASCB);
     51 }
     52 
     53 static uint32_t
     54 amdccp_rnd_read(struct amdccp_softc *sc)
     55 {
     56 	size_t retries = 5;
     57 	uint32_t bits;
     58 
     59 	/* TRNG register reads 0x0 when bits aren't valid */
     60 	while (retries--) {
     61 		bits = bus_space_read_4(sc->sc_bst, sc->sc_bsh, CCP_TRNG_REG);
     62 		if (bits != 0x0)
     63 			break;
     64 	}
     65 
     66 	return bits;
     67 }
     68 
     69 static void
     70 amdccp_rnd_callback(size_t bytes_wanted, void *priv)
     71 {
     72 	struct amdccp_softc * const sc = priv;
     73 	uint32_t buf[128];
     74 	size_t cnt;
     75 
     76 	while (bytes_wanted) {
     77 		const size_t nbytes = MIN(bytes_wanted, sizeof(buf));
     78 		const size_t nwords = howmany(nbytes, sizeof(buf[0]));
     79 
     80 		for (cnt = 0; cnt < nwords; cnt++) {
     81 			buf[cnt] = amdccp_rnd_read(sc);
     82 			if (buf[cnt] == 0) {
     83 				break;
     84 			}
     85 		}
     86 		if (cnt == 0) {
     87 			break;
     88 		}
     89 
     90 		const size_t cntby = cnt * sizeof(buf[0]);
     91 
     92 		rnd_add_data_sync(&sc->sc_rndsource, buf, cntby, cntby * NBBY);
     93 		bytes_wanted -= MIN(bytes_wanted, cntby);
     94 	}
     95 	explicit_memset(buf, 0, sizeof(buf));
     96 }
     97