linux-kernel - Re: [RFC PATCH 01/17] net: ipa: Correct ipa_status

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Date:   Wed, 13 Oct 2021 17:28:28 -0500
From:   Alex Elder <elder@...e.org>
To:     Sireesh Kodali <sireeshkodali1@...il.com>,
        phone-devel@...r.kernel.org, ~postmarketos/upstreaming@...ts.sr.ht,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, elder@...nel.org
Cc:     Vladimir Lypak <vladimir.lypak@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [RFC PATCH 01/17] net: ipa: Correct ipa_status_opcode enumeration

On 9/19/21 10:07 PM, Sireesh Kodali wrote:
> From: Vladimir Lypak <vladimir.lypak@...il.com>
> 
> The values in the enumaration were defined as bitmasks (base 2 exponents of
> actual opcodes). Meanwhile, it's used not as bitmask
> ipa_endpoint_status_skip and ipa_status_formet_packet functions (compared
> directly with opcode from status packet). This commit converts these values
> to actual hardware constansts.
> 
> Signed-off-by: Vladimir Lypak <vladimir.lypak@...il.com>
> Signed-off-by: Sireesh Kodali <sireeshkodali1@...il.com>
> ---
>   drivers/net/ipa/ipa_endpoint.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ipa/ipa_endpoint.c b/drivers/net/ipa/ipa_endpoint.c
> index 5528d97110d5..29227de6661f 100644
> --- a/drivers/net/ipa/ipa_endpoint.c
> +++ b/drivers/net/ipa/ipa_endpoint.c
> @@ -41,10 +41,10 @@
>   
>   /** enum ipa_status_opcode - status element opcode hardware values */
>   enum ipa_status_opcode {
> -	IPA_STATUS_OPCODE_PACKET		= 0x01,
> -	IPA_STATUS_OPCODE_DROPPED_PACKET	= 0x04,
> -	IPA_STATUS_OPCODE_SUSPENDED_PACKET	= 0x08,
> -	IPA_STATUS_OPCODE_PACKET_2ND_PASS	= 0x40,
> +	IPA_STATUS_OPCODE_PACKET		= 0,
> +	IPA_STATUS_OPCODE_DROPPED_PACKET	= 2,
> +	IPA_STATUS_OPCODE_SUSPENDED_PACKET	= 3,
> +	IPA_STATUS_OPCODE_PACKET_2ND_PASS	= 6,

I haven't looked at how these symbols are used (whether you
changed it at all), but I'm pretty sure this is wrong.

The downstream tends to define "soft" symbols that must
be mapped to their hardware equivalent values.  So for
example you might find a function ipa_pkt_status_parse()
that translates between the hardware status structure
and the abstracted "soft" status structure.  In that
function you see, for example, that hardware status
opcode 0x1 is translated to IPAHAL_PKT_STATUS_OPCODE_PACKET,
which downstream is defined to have value 0.

In many places the upstream code eliminates that layer
of indirection where possible.  So enumerated constants
are assigned specific values that match what the hardware
uses.

					-Alex

>   };
>   
>   /** enum ipa_status_exception - status element exception type */
>