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([2001:470:dd84:abc0::8a5]) by smtp.gmail.com with ESMTPSA id v2sm365110ljg.46.2021.12.15.02.37.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 15 Dec 2021 02:37:27 -0800 (PST) Message-ID: <67a77fc5-6db4-ba26-cacb-9758336ad074@linaro.org> Date: Wed, 15 Dec 2021 13:37:24 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.2 Subject: Re: [PATCH 4.19 29/74] clk: qcom: regmap-mux: fix parent clock lookup Content-Language: en-GB To: Pavel Machek , Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Stephen Boyd References: <20211213092930.763200615@linuxfoundation.org> <20211213092931.784850569@linuxfoundation.org> <20211215091623.GA15796@amd> From: Dmitry Baryshkov In-Reply-To: <20211215091623.GA15796@amd> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/12/2021 12:16, Pavel Machek wrote: > Hi! > >> The function mux_get_parent() uses qcom_find_src_index() to find the >> parent clock index, which is incorrect: qcom_find_src_index() uses src >> enum for the lookup, while mux_get_parent() should use cfg field (which >> corresponds to the register value). Add qcom_find_cfg_index() function >> doing this kind of lookup and use it for mux parent lookup. > > This appears to have problems with error handling. > >> +++ b/drivers/clk/qcom/clk-regmap-mux.c >> @@ -36,7 +36,7 @@ static u8 mux_get_parent(struct clk_hw * >> val &= mask; >> >> if (mux->parent_map) >> - return qcom_find_src_index(hw, mux->parent_map, val); >> + return qcom_find_cfg_index(hw, mux->parent_map, val); >> >> return val; >> } > > So this returns u8. > >> +int qcom_find_cfg_index(struct clk_hw *hw, const struct parent_map *map, u8 cfg) >> +{ >> + int i, num_parents = clk_hw_get_num_parents(hw); >> + >> + for (i = 0; i < num_parents; i++) >> + if (cfg == map[i].cfg) >> + return i; >> + >> + return -ENOENT; >> +} > > In case of error, -ENOENT will be cast to u8 in caller. I don't > believe that is correct. Unfortunately there is no way to return proper error code from clk_ops->get_parent() callback. However returning -ENOENT would translate to 254. Then clk_core_get_parent_by_index() would determine that there is no such parent and return NULL. A call to clk_set_parent would reparent the clock. Returning some sensible default (e.g. 0) would be much worse, since then the clock subsystem would assume that the clock has correct parent. A call to clk_set_parent would always result in ops->set_parent() call, reparenting the clock correctly. Most probably it would be correct to make ops->get_parent() return int instead of u8 (either an index or an -ERROR). However this was out of scope for this patch. -- With best wishes Dmitry