all: Add GPU mining, disabled by default

cmd/geth/main.go

@@ -104,6 +104,22 @@ The makedag command generates an ethash DAG in /tmp/dag.
 
 This command exists to support the system testing project.
 Regular users do not need to execute it.
+`,
+		},
+		{
+			Action: gpuinfo,
+			Name:   "gpuinfo",
+			Usage:  "gpuinfo",
+			Description: `
+Prints OpenCL device info for all found GPUs.
+`,
+		},
+		{
+			Action: gpubench,
+			Name:   "gpubench",
+			Usage:  "benchmark GPU",
+			Description: `
+Runs quick benchmark on first GPU found.
 `,
 		},
 		{
@@ -298,6 +314,7 @@ JavaScript API. See https://github.com/ethereum/go-ethereum/wiki/Javascipt-Conso
 		utils.GasPriceFlag,
 		utils.MinerThreadsFlag,
 		utils.MiningEnabledFlag,
+		utils.MiningGPUFlag,
 		utils.AutoDAGFlag,
 		utils.NATFlag,
 		utils.NatspecEnabledFlag,
@@ -586,7 +603,10 @@ func startEth(ctx *cli.Context, eth *eth.Ethereum) {
 		}
 	}
 	if ctx.GlobalBool(utils.MiningEnabledFlag.Name) {
-		if err := eth.StartMining(ctx.GlobalInt(utils.MinerThreadsFlag.Name)); err != nil {
+		err := eth.StartMining(
+			ctx.GlobalInt(utils.MinerThreadsFlag.Name),
+			ctx.GlobalString(utils.MiningGPUFlag.Name))
+		if err != nil {
 			utils.Fatalf("%v", err)
 		}
 	}
@@ -740,6 +760,29 @@ func makedag(ctx *cli.Context) {
 	}
 }
 
+func gpuinfo(ctx *cli.Context) {
+	eth.PrintOpenCLDevices()
+}
+
+func gpubench(ctx *cli.Context) {
+	args := ctx.Args()
+	wrongArgs := func() {
+		utils.Fatalf(`Usage: geth gpubench <gpu number>`)
+	}
+	switch {
+	case len(args) == 1:
+		n, err := strconv.ParseUint(args[0], 0, 64)
+		if err != nil {
+			wrongArgs()
+		}
+		eth.GPUBench(n)
+	case len(args) == 0:
+		eth.GPUBench(0)
+	default:
+		wrongArgs()
+	}
+}
+
 func version(c *cli.Context) {
 	fmt.Println(ClientIdentifier)
 	fmt.Println("Version:", Version)