Re: [PATCH v2 1/6] linux/log2.h: Add roundup/rounddown_pow_two64() family of functions

[Andrew Murray]

On Tue, Nov 12, 2019 at 04:59:20PM +0100, Nicolas Saenz Julienne wrote:
> Some users need to make sure their rounding function accepts and returns
> 64bit long variables regardless of the architecture. Sadly
> roundup/rounddown_pow_two() takes and returns unsigned longs. Create a
> new generic 64bit variant of the function and cleanup rougue custom
> implementations.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
> ---
>  drivers/net/ethernet/mellanox/mlx4/en_clock.c |  3 +-
>  drivers/pci/controller/pcie-cadence-ep.c      |  7 +--
>  drivers/pci/controller/pcie-cadence.c         |  7 +--
>  drivers/pci/controller/pcie-rockchip-ep.c     |  9 ++--

Thanks for making this change. See comments inline...

>  include/linux/log2.h                          | 52 +++++++++++++++++++
>  kernel/dma/direct.c                           |  3 +-
>  6 files changed, 63 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_clock.c b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
> index 024788549c25..027bd72505e2 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_clock.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
> @@ -33,6 +33,7 @@
>  
>  #include <linux/mlx4/device.h>
>  #include <linux/clocksource.h>
> +#include <linux/log2.h>
>  
>  #include "mlx4_en.h"
>  
> @@ -252,7 +253,7 @@ static u32 freq_to_shift(u16 freq)
>  {
>  	u32 freq_khz = freq * 1000;
>  	u64 max_val_cycles = freq_khz * 1000 * MLX4_EN_WRAP_AROUND_SEC;
> -	u64 max_val_cycles_rounded = 1ULL << fls64(max_val_cycles - 1);
> +	u64 max_val_cycles_rounded = roundup_pow_of_two64(max_val_cycles);
>  	/* calculate max possible multiplier in order to fit in 64bit */
>  	u64 max_mul = div64_u64(ULLONG_MAX, max_val_cycles_rounded);
>  
> diff --git a/drivers/pci/controller/pcie-cadence-ep.c b/drivers/pci/controller/pcie-cadence-ep.c
> index def7820cb824..26ff424b16f5 100644
> --- a/drivers/pci/controller/pcie-cadence-ep.c
> +++ b/drivers/pci/controller/pcie-cadence-ep.c
> @@ -10,6 +10,7 @@
>  #include <linux/platform_device.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/sizes.h>
> +#include <linux/log2.h>
>  
>  #include "pcie-cadence.h"
>  
> @@ -90,11 +91,7 @@ static int cdns_pcie_ep_set_bar(struct pci_epc *epc, u8 fn,
>  
>  	/* BAR size is 2^(aperture + 7) */
>  	sz = max_t(size_t, epf_bar->size, CDNS_PCIE_EP_MIN_APERTURE);
> -	/*
> -	 * roundup_pow_of_two() returns an unsigned long, which is not suited
> -	 * for 64bit values.
> -	 */
> -	sz = 1ULL << fls64(sz - 1);
> +	sz = roundup_pow_of_two64(sz);
>  	aperture = ilog2(sz) - 7; /* 128B -> 0, 256B -> 1, 512B -> 2, ... */
>  
>  	if ((flags & PCI_BASE_ADDRESS_SPACE) == PCI_BASE_ADDRESS_SPACE_IO) {
> diff --git a/drivers/pci/controller/pcie-cadence.c b/drivers/pci/controller/pcie-cadence.c
> index cd795f6fc1e2..b2278e6b955c 100644
> --- a/drivers/pci/controller/pcie-cadence.c
> +++ b/drivers/pci/controller/pcie-cadence.c
> @@ -4,6 +4,7 @@
>  // Author: Cyrille Pitchen <cyrille.pitchen@xxxxxxxxxxxxxxxxxx>
>  
>  #include <linux/kernel.h>
> +#include <linux/log2.h>
>  
>  #include "pcie-cadence.h"
>  
> @@ -11,11 +12,7 @@ void cdns_pcie_set_outbound_region(struct cdns_pcie *pcie, u8 fn,
>  				   u32 r, bool is_io,
>  				   u64 cpu_addr, u64 pci_addr, size_t size)
>  {
> -	/*
> -	 * roundup_pow_of_two() returns an unsigned long, which is not suited
> -	 * for 64bit values.
> -	 */
> -	u64 sz = 1ULL << fls64(size - 1);
> +	u64 sz = roundup_pow_of_two64(size);
>  	int nbits = ilog2(sz);
>  	u32 addr0, addr1, desc0, desc1;
>  
> diff --git a/drivers/pci/controller/pcie-rockchip-ep.c b/drivers/pci/controller/pcie-rockchip-ep.c
> index d743b0a48988..ed50aaf27784 100644
> --- a/drivers/pci/controller/pcie-rockchip-ep.c
> +++ b/drivers/pci/controller/pcie-rockchip-ep.c
> @@ -16,6 +16,7 @@
>  #include <linux/platform_device.h>
>  #include <linux/pci-epf.h>
>  #include <linux/sizes.h>
> +#include <linux/log2.h>
>  
>  #include "pcie-rockchip.h"
>  
> @@ -70,7 +71,7 @@ static void rockchip_pcie_prog_ep_ob_atu(struct rockchip_pcie *rockchip, u8 fn,
>  					 u32 r, u32 type, u64 cpu_addr,
>  					 u64 pci_addr, size_t size)
>  {
> -	u64 sz = 1ULL << fls64(size - 1);
> +	u64 sz = roundup_pow_of_two64(size);
>  	int num_pass_bits = ilog2(sz);
>  	u32 addr0, addr1, desc0, desc1;
>  	bool is_nor_msg = (type == AXI_WRAPPER_NOR_MSG);
> @@ -172,11 +173,7 @@ static int rockchip_pcie_ep_set_bar(struct pci_epc *epc, u8 fn,
>  	/* BAR size is 2^(aperture + 7) */
>  	sz = max_t(size_t, epf_bar->size, MIN_EP_APERTURE);
>  
> -	/*
> -	 * roundup_pow_of_two() returns an unsigned long, which is not suited
> -	 * for 64bit values.
> -	 */
> -	sz = 1ULL << fls64(sz - 1);
> +	sz = roundup_pow_of_two64(sz);
>  	aperture = ilog2(sz) - 7; /* 128B -> 0, 256B -> 1, 512B -> 2, ... */
>  
>  	if ((flags & PCI_BASE_ADDRESS_SPACE) == PCI_BASE_ADDRESS_SPACE_IO) {
> diff --git a/include/linux/log2.h b/include/linux/log2.h
> index 83a4a3ca3e8a..db12d92ab6eb 100644
> --- a/include/linux/log2.h
> +++ b/include/linux/log2.h
> @@ -67,6 +67,24 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
>  	return 1UL << (fls_long(n) - 1);
>  }
>  
> +/**
> + * __roundup_pow_of_two64() - round 64bit value up to nearest power of two
> + * @n: value to round up
> + */
> +static inline __attribute__((const)) __u64 __roundup_pow_of_two64(__u64 n)

To be consistent with other functions in the same file (__ilog_u64) you may
want to rename this to __roundup_pow_of_two_u64.

Also do you know why u64 is used in some places and __u64 in others?

> +{
> +	return 1UL << fls64(n - 1);

Does this need to be (and for the others):

return 1ULL << fls64(n - 1);

Notice that the PCI drivers you convert, all use 1ULL.

Thanks,

Andrew Murray 


> +}
> +
> +/**
> + * __rounddown_pow_of_two64() - round 64bit value down to nearest power of two
> + * @n: value to round down
> + */
> +static inline __attribute__((const)) __u64 __rounddown_pow_of_two64(__u64 n)
> +{
> +	return 1UL << (fls64(n) - 1);
> +}
> +
>  /**
>   * const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value
>   * @n: parameter
> @@ -194,6 +212,40 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
>  	__rounddown_pow_of_two(n)		\
>   )
>  
> +/**
> + * roundup_pow_of_two64 - round the given 64bit value up to nearest power of
> + * two
> + * @n: parameter
> + *
> + * round the given value up to the nearest power of two
> + * - the result is undefined when n == 0
> + * - this can be used to initialise global variables from constant data
> + */
> +#define roundup_pow_of_two64(n)			\
> +(						\
> +	__builtin_constant_p(n) ? (		\
> +		(n == 1) ? 1 :			\
> +		(1UL << (ilog2((n) - 1) + 1))	\
> +				   ) :		\
> +	__roundup_pow_of_two64(n)		\
> +)
> +
> +/**
> + * rounddown_pow_of_two64 - round the given 64bit value down to nearest power
> + * of two
> + * @n: parameter
> + *
> + * round the given value down to the nearest power of two
> + * - the result is undefined when n == 0
> + * - this can be used to initialise global variables from constant data
> + */
> +#define rounddown_pow_of_two64(n)		\
> +(						\
> +	__builtin_constant_p(n) ? (		\
> +		(1UL << ilog2(n))) :		\
> +	__rounddown_pow_of_two64(n)		\
> +)
> +
>  static inline __attribute_const__
>  int __order_base_2(unsigned long n)
>  {
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index b9e1744999d9..a419530abd3e 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -15,6 +15,7 @@
>  #include <linux/vmalloc.h>
>  #include <linux/set_memory.h>
>  #include <linux/swiotlb.h>
> +#include <linux/log2.h>
>  
>  /*
>   * Most architectures use ZONE_DMA for the first 16 Megabytes, but some use it
> @@ -53,7 +54,7 @@ u64 dma_direct_get_required_mask(struct device *dev)
>  {
>  	u64 max_dma = phys_to_dma_direct(dev, (max_pfn - 1) << PAGE_SHIFT);
>  
> -	return (1ULL << (fls64(max_dma) - 1)) * 2 - 1;
> +	return rounddown_pow_of_two64(max_dma) * 2 - 1;
>  }
>  
>  static gfp_t __dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask,
> -- 
> 2.24.0
>