Re: [PATCH] ahci: print the number of implemented ports

[Sergei Shtylyov <sergei.shtylyov@gmail.com>]

On 2/14/24 9:20 PM, Niklas Cassel wrote:

> We are currently printing the CAP.NP field.
> CAP.NP is a 0's based value indicating the maximum number of ports
> supported by the HBA silicon. Note that the number of ports indicated
> in this field may be more than the number of ports indicated in the
> PI (ports implemented) register. (See AHCI 1.3.1, section 3.1.1 -
> Offset 00h: CAP – HBA Capabilities.)
> 
> Print the port_map instead, which is the value read by the PI (ports
> implemented) register (after fixups).
> 
> PI (ports implemented) register is a field that has a bit set to '1'
> if that specific port is implemented. This register is allowed to have
> zeroes mixed with ones, i.e. a port in the middle is allowed to be
> unimplemented. (See AHCI 1.3.1, section 3.1.4 - Offset 0Ch: PI – Ports
> Implemented.)
> 
> Fix the libata print to only print the number of implemented ports,
> instead of the theoretical number of ports supported by the HBA.
> 
> Suggested-by: Damien Le Moal <dlemoal@kernel.org>
> Signed-off-by: Niklas Cassel <cassel@kernel.org>
> ---
>  drivers/ata/ahci.h    | 11 +++++++++++
>  drivers/ata/libahci.c |  2 +-
>  2 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/ata/ahci.h b/drivers/ata/ahci.h
> index df8f8a1a3a34..92d29a059763 100644
> --- a/drivers/ata/ahci.h
> +++ b/drivers/ata/ahci.h
> @@ -455,4 +455,15 @@ static inline int ahci_nr_ports(u32 cap)
>  	return (cap & 0x1f) + 1;
>  }
>  
> +static inline int ahci_nr_ports_in_map(u32 map)
> +{
> +	unsigned long port_map = map;

   Why cast to potentially 64-bit type?

> +	int i, n = 0;
> +
> +	for_each_set_bit(i, &port_map, AHCI_MAX_PORTS)
> +		n++;

   There's hweight32() for that, IIUC.

> +
> +	return n;
> +}
> +
>  #endif /* _AHCI_H */
[...]

MBR, Sergey