smbus: Fix spd_data_generate() error API violation

The Error ** argument must be NULL, &error_abort, &error_fatal, or a
pointer to a variable containing NULL.  Passing an argument of the
latter kind twice without clearing it in between is wrong: if the
first call sets an error, it no longer points to NULL for the second
call.

spd_data_generate() can pass @errp to error_setg() more than once when
it adjusts both memory size and type.  Harmless, because no caller
passes anything that needs adjusting.  Until the previous commit,
sam460ex passed types that needed adjusting, but not sizes.

spd_data_generate()'s contract is rather awkward:

    If everything's fine, return non-null and don't set an error.

    Else, if memory size or type need adjusting, return non-null and
    set an error describing the adjustment.

    Else, return null and set an error reporting why no data can be
    generated.

Its callers treat the error as a warning even when null is returned.
They don't create the "smbus-eeprom" device then.  Suspicious.

Since the previous commit, only "everything's fine" can actually
happen.  Drop the unused code and simplify the callers.  This gets rid
of the error API violation.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200422134815.1584-3-armbru@redhat.com>

hw/i2c/smbus_eeprom.c

@@ -195,8 +195,7 @@ void smbus_eeprom_init(I2CBus *smbus, int nb_eeprom,
 }
 
 /* Generate SDRAM SPD EEPROM data describing a module of type and size */
-uint8_t *spd_data_generate(enum sdram_type type, ram_addr_t ram_size,
-                           Error **errp)
+uint8_t *spd_data_generate(enum sdram_type type, ram_addr_t ram_size)
 {
     uint8_t *spd;
     uint8_t nbanks;
@@ -222,29 +221,10 @@ uint8_t *spd_data_generate(enum sdram_type type, ram_addr_t ram_size,
         g_assert_not_reached();
     }
     size = ram_size >> 20; /* work in terms of megabytes */
-    if (size < 4) {
-        error_setg(errp, "SDRAM size is too small");
-        return NULL;
-    }
     sz_log2 = 31 - clz32(size);
     size = 1U << sz_log2;
-    if (ram_size > size * MiB) {
-        error_setg(errp, "SDRAM size 0x"RAM_ADDR_FMT" is not a power of 2, "
-                   "truncating to %u MB", ram_size, size);
-    }
-    if (sz_log2 < min_log2) {
-        error_setg(errp,
-                   "Memory size is too small for SDRAM type, adjusting type");
-        if (size >= 32) {
-            type = DDR;
-            min_log2 = 5;
-            max_log2 = 12;
-        } else {
-            type = SDR;
-            min_log2 = 2;
-            max_log2 = 9;
-        }
-    }
+    assert(ram_size == size * MiB);
+    assert(sz_log2 >= min_log2);
 
     nbanks = 1;
     while (sz_log2 > max_log2 && nbanks < 8) {
@@ -252,9 +232,7 @@ uint8_t *spd_data_generate(enum sdram_type type, ram_addr_t ram_size,
         nbanks++;
     }
 
-    if (size > (1ULL << sz_log2) * nbanks) {
-        error_setg(errp, "Memory size is too big for SDRAM, truncating");
-    }
+    assert(size == (1ULL << sz_log2) * nbanks);
 
     /* split to 2 banks if possible to avoid a bug in MIPS Malta firmware */
     if (nbanks == 1 && sz_log2 > min_log2) {

hw/mips/mips_fulong2e.c

@@ -297,7 +297,6 @@ static void mips_fulong2e_init(MachineState *machine)
     MemoryRegion *bios = g_new(MemoryRegion, 1);
     long bios_size;
     uint8_t *spd_data;
-    Error *err = NULL;
     int64_t kernel_entry;
     PCIBus *pci_bus;
     ISABus *isa_bus;
@@ -377,13 +376,8 @@ static void mips_fulong2e_init(MachineState *machine)
     }
 
     /* Populate SPD eeprom data */
-    spd_data = spd_data_generate(DDR, machine->ram_size, &err);
-    if (err) {
-        warn_report_err(err);
-    }
-    if (spd_data) {
-        smbus_eeprom_init_one(smbus, 0x50, spd_data);
-    }
+    spd_data = spd_data_generate(DDR, machine->ram_size);
+    smbus_eeprom_init_one(smbus, 0x50, spd_data);
 
     mc146818_rtc_init(isa_bus, 2000, NULL);
 

hw/ppc/sam460ex.c

@@ -292,7 +292,6 @@ static void sam460ex_init(MachineState *machine)
     SysBusDevice *sbdev;
     struct boot_info *boot_info;
     uint8_t *spd_data;
-    Error *err = NULL;
     int success;
 
     cpu = POWERPC_CPU(cpu_create(machine->cpu_type));
@@ -336,14 +335,9 @@ static void sam460ex_init(MachineState *machine)
     i2c = PPC4xx_I2C(dev)->bus;
     /* SPD EEPROM on RAM module */
     spd_data = spd_data_generate(ram_sizes[0] < 128 * MiB ? DDR : DDR2,
-                                 ram_sizes[0], &err);
-    if (err) {
-        warn_report_err(err);
-    }
-    if (spd_data) {
-        spd_data[20] = 4; /* SO-DIMM module */
-        smbus_eeprom_init_one(i2c, 0x50, spd_data);
-    }
+                                 ram_sizes[0]);
+    spd_data[20] = 4; /* SO-DIMM module */
+    smbus_eeprom_init_one(i2c, 0x50, spd_data);
     /* RTC */
     i2c_create_slave(i2c, "m41t80", 0x68);
 

include/hw/i2c/smbus_eeprom.h

@@ -31,6 +31,6 @@ void smbus_eeprom_init(I2CBus *bus, int nb_eeprom,
                        const uint8_t *eeprom_spd, int size);
 
 enum sdram_type { SDR = 0x4, DDR = 0x7, DDR2 = 0x8 };
-uint8_t *spd_data_generate(enum sdram_type type, ram_addr_t size, Error **errp);
+uint8_t *spd_data_generate(enum sdram_type type, ram_addr_t size);
 
 #endif