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[124.171.83.152]) by smtp.gmail.com with ESMTPSA id i22sm15191430pfo.92.2020.06.22.19.29.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 Jun 2020 19:29:20 -0700 (PDT) Subject: Re: [PATCH 1/4] powerpc/pseries/iommu: Update call to ibm,query-pe-dma-windows To: Leonardo Bras Cc: Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Thiago Jung Bauermann , Ram Pai , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org References: <20200619050619.266888-1-leobras.c@gmail.com> <20200619050619.266888-2-leobras.c@gmail.com> <4176ea2b-c778-2f59-ba57-7339b873ead5@ozlabs.ru> From: Alexey Kardashevskiy Autocrypt: addr=aik@ozlabs.ru; keydata= mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD EePO1JqpVuIow/wGud9xaPA5uvuVgRS1q7RU8otD+7VLDFzPRiRE4Jfr2CW89Ox6BF+q5ZPV /pS4v4G9eOrw1v09lEKHB9WtiBVhhxKK1LnUjPEH3ifkOkgW7jFfoYgTdtB3XaXVgYnNPDFo PTBYsJy+wr89XfyHr2Ev7BB3Xaf7qICXdBF8MEVY8t/UFsesg4wFWOuzCfqxFmKEaPDZlTuR 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c7E5M+/NpslPCmYnDjs5qg0/3ihh6XuOGggZQOqrYPC3PnsNs3NxirwOkVPQgO6mXxpuifvJ DG9EMkK8IBXnLulqVk54kf7fE0jT/d8RTtJIA92GzsgdK2rpT1MBKKVffjRFGwN7nQVOzi4T XrB5p+6ML7Bd84xOEGsj/vdaXmz1esuH7BOZAGEZfLRCHJ0GVCSssg== Message-ID: <8b7482b4-ec5d-3c20-a5b7-3456e7592d6d@ozlabs.ru> Date: Tue, 23 Jun 2020 12:29:15 +1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23/06/2020 12:14, Leonardo Bras wrote: > On Tue, 2020-06-23 at 11:12 +1000, Alexey Kardashevskiy wrote: > [snip] >>>>> +static int query_ddw_out_sz(struct device_node *par_dn) >>>> >>>> Can easily be folded into query_ddw(). >>> >>> Sure, but it will get inlined by the compiler, and I think it reads >>> better this way. >>> I mean, I understand you have a reason to think it's better to fold it >>> in query_ddw(), and I would like to better understand that to improve >>> my code in the future. >> >> You have numbers 5 and 6 (the number of parameters) twice in the file, >> this is why I brought it up. query_ddw_out_sz() can potentially return >> something else than 5 or 6 and you will have to change the callsite(s) >> then, since these are not macros, this allows to think there may be more >> places with 5 and 6. Dunno. A single function will simplify things imho. > > That's a good point. Thanks! > >> >> >>>>> +{ >>>>> + int ret; >>>>> + u32 ddw_ext[3]; >>>>> + >>>>> + ret = of_property_read_u32_array(par_dn, "ibm,ddw-extensions", >>>>> + &ddw_ext[0], 3); >>>>> + if (ret || ddw_ext[0] < 2 || ddw_ext[2] != 1) >>>> >>>> Oh that PAPR thing again :-/ >>>> >>>> === >>>> The “ibm,ddw-extensions” property value is a list of integers the first >>>> integer indicates the number of extensions implemented and subsequent >>>> integers, one per extension, provide a value associated with that >>>> extension. >>>> === >>>> >>>> So ddw_ext[0] is length. >>>> Listindex==2 is for "reset" says PAPR and >>>> Listindex==3 is for this new 64bit "largest_available_block". >>>> >>>> So I'd expect ddw_ext[2] to have the "reset" token and ddw_ext[3] to >>>> have "1" for this new feature but indexes are smaller. I am confused. >>>> Either way these "2" and "3" needs to be defined in macros, "0" probably >>>> too. >>> >>> Remember these indexes are not C-like 0-starting indexes, where the >>> size would be Listindex==1. >> >> Yeah I can see that is the assumption but out of curiosity - is it >> written anywhere? Across PAPR, they index bytes from 1 but bits from 0 :-/ > > From LoPAR: > The “ibm,ddw-extensions” property value is a list of integers the first > integer indicates the number of extensions implemented and subsequent > integers, one per extension, provide a value associated with that > extension. > > And the list/table then shows extensions from 2 on onwards: > List index 2 : Token of the ibm,reset-pe-dma-windows RTAS Call > (...) I means a place saying "we number things starting from 1 and not from zero", this kind of thing. The code implementing the spec uses the C language so it would make sense to count from zero, otoh the writer probably did not write any code for ages :) -- Alexey