clk: at91: modify PMC peripheral clock to deal with newer register layout

As some more information is added to the PCR register, we'd better use
a copy of its content and modify just the peripheral-related bits.
Implement a read-modify-write for the enable() and disable() callbacks.

Signed-off-by: Nicolas Ferre <[e-mail]>
Signed-off-by: Boris Brezillon <[e-mail]>
Signed-off-by: Stephen Boyd <[e-mail]>

drivers/clk/at91/clk-peripheral.c

···
 {
 	struct clk_sam9x5_peripheral *periph = to_clk_sam9x5_peripheral(hw);
 	struct at91_pmc *pmc = periph->pmc;
+	u32 tmp;
 
 	if (periph->id < PERIPHERAL_ID_MIN)
 		return 0;
 
-	pmc_write(pmc, AT91_PMC_PCR, (periph->id & AT91_PMC_PCR_PID_MASK) |
-				     AT91_PMC_PCR_CMD |
-				     AT91_PMC_PCR_DIV(periph->div) |
-				     AT91_PMC_PCR_EN);
+	pmc_lock(pmc);
+	pmc_write(pmc, AT91_PMC_PCR, (periph->id & AT91_PMC_PCR_PID_MASK));
+	tmp = pmc_read(pmc, AT91_PMC_PCR) & ~AT91_PMC_PCR_DIV_MASK;
+	pmc_write(pmc, AT91_PMC_PCR, tmp | AT91_PMC_PCR_DIV(periph->div)
+					 | AT91_PMC_PCR_CMD
+					 | AT91_PMC_PCR_EN);
+	pmc_unlock(pmc);
 	return 0;
 }
 
···
 {
 	struct clk_sam9x5_peripheral *periph = to_clk_sam9x5_peripheral(hw);
 	struct at91_pmc *pmc = periph->pmc;
+	u32 tmp;
 
 	if (periph->id < PERIPHERAL_ID_MIN)
 		return;
 
-	pmc_write(pmc, AT91_PMC_PCR, (periph->id & AT91_PMC_PCR_PID_MASK) |
-				     AT91_PMC_PCR_CMD);
+	pmc_lock(pmc);
+	pmc_write(pmc, AT91_PMC_PCR, (periph->id & AT91_PMC_PCR_PID_MASK));
+	tmp = pmc_read(pmc, AT91_PMC_PCR) & ~AT91_PMC_PCR_EN;
+	pmc_write(pmc, AT91_PMC_PCR, tmp | AT91_PMC_PCR_CMD);
+	pmc_unlock(pmc);
 }
 
 static int clk_sam9x5_peripheral_is_enabled(struct clk_hw *hw)